Post-War universe

After the end of the War in Heaven and erasure of its associated timeline, a new state of reality was established, characterised by the lack of Gallifrey and most members of major war-time powers, resulting in vast changes in the nature of reality, and many new powers attempting to rise up and take their place.

Nature
The disappearance of the Time Lords from history had great consequences. One of these consequences was the breakdown of universal "laws," filling the universe with irrationality, ritualism, and magic. (The Adventuress of Henrietta Street) The Eighth Doctor frequently came against magic and mysticism as often as he did science and technology during this period (PROSE: The Burning, The City of the Dead, Grimm Reality, The Adventuress of Henrietta Street, Mad Dogs and Englishmen, Camera Obscura, et al). Creatures such as Water elementals and magicians, who would not have existed under the Time Lords' laws, thrived. This rampant irrationality and magic harkened back to (PROSE: The City of the Dead) the Carnival Queen's descriptions of the Dark Times. (PROSE: Christmas on a Rational Planet'')

Another consequence was time travel technology becoming more widespread throughout the universe. (PROSE: The Adventuress of Henrietta Street, Eater of Wasps, Trading Futures, The Book of the Still, Mad Dogs and Englishmen, Camera Obscura) Rudimentary knowledge of time worked its way into eighteenth century Earth culture, including in groups like the Hellfire Club, the Freemasons, the Eriticy, and the Service. (PROSE: The Adventuress of Henrietta Street) In 1774, American Freemasons fought Faction Paradox for control of Earth's history at King George III's 1774 mammoth hunt. (COMIC: Political Animals, Bêtes Noires & Dark Horses)

A new order
When the Eighth Doctor emerged from his century-long exile on Earth (PROSE: The Burning, Escape Velocity) after destroying Romana III's Gallifrey, (PROSE: The Ancestor Cell) he discovered that Gallifrey and the Time Lords had been completely wiped from history. (PROSE: The Adventuress of Henrietta Street) Despite this, there still existed four remaining Time Lords, (PROSE: The Adventuress of Henrietta Street, Trading Futures, The Gallifrey Chronicles) though they were forced by their new circumstances to remove their second hearts that were connecting them to their disappeared homeworld. (PROSE: The Adventuress of Henrietta Street, Timeless)

Survivance of War-time powers
Several other groups from the War survived its ending, including Faction Paradox and (COMIC: Political Animals) the Mayakai. (PROSE: The Adventuress of Henrietta Street, COMIC: Political Animals) While there were only four "elementals," the Doctor encountered other Gallifreyan survivors such as Chloe and Erasmus (PROSE: Timeless) and Marnal. (PROSE: The Gallifrey Chronicles) It was implied that Romana had managed to survive and live on to regenerate a fourth time (PROSE: Tomb of Valdemar) despite the obliteration of her Gallifrey. (PROSE: The Ancestor Cell)

Emergence of new powers
After the destruction of Gallifrey, "temporal tourism" into earlier eras of its history became popular, although it was a risky hobby. Tourism into the War era itself was inadvisable, however, and increasingly difficult as the War kept reiterating and looping on itself as the Time Lords and Enemy tried to undercut each other, becoming shorter and more violent each time. (PROSE: Gallifrey: A Rough Guide)

Emboldened by their new knowledge, several groups or individuals went so far as to try to fill the void left by the Time Lords by seizing control of history. The Onihr scavenged fragments of time travel technology for thousands of years in their quest to discover the secrets of time travel and become Lords of Time. (PROSE: Trading Futures) Sabbath, an agent of the Service who briefly became a servant of the Great Houses in the War, (AUDIO: In the Year of the Cat) stole the Eighth Doctor's second heart to gain some Time Lord abilities, (PROSE: The Adventuress of Henrietta Street) and he planned to use them to replace Gallifrey and the Time Lords with Earth and humanity. (PROSE: The Adventuress of Henrietta Street, Timeless) In their own quest to become the new Lords of Time, the Council of Eight eliminated their enemies from their fortress in the Time Vortex by manipulating both Sabbath (PROSE: Sometime Never...) and the Doctor. (PROSE: Anachrophobia) However, they were defeated by the Doctor working together with Sabbath and Miranda. (PROSE: Sometime Never...)

The Daleks, often previously assumed to be the enemy, (PROSE: The Book of the Enemy) rose to prominence in the Time Lords' absence, crossing paths with the Doctor, Fitz, and Trix several times. (PROSE: The Gallifrey Chronicles) They monitored the Council of Eight's affairs and watched the destruction of the Time Station, plotting how they could take advantage of events for their own ends. (PROSE: Sometime Never...) The Doctor foiled their attempt to exterminate the Pope of 2097 on a visit to Mars, a crucial nexus point of human history. (PROSE: The Gallifrey Chronicles)

Endpoints
During his wanderings in the post-War universe, the amnesiac Eighth Doctor encountered visions, predictions and testimonies about several different futures for himself and the universe at large. (PROSE: The Tomorrow Windows, Father Time, The Gallifrey Chronicles)

The Needle and the Greyness
After suffering from amnesia for several years, (PROSE: The Burning, et al) the Eighth Doctor foresaw, and encountered evidence of, a distant future of the post-War universe in which, although Gallifrey was not restored, he and other Time Lords regained control of the universe and attempted to stabilise it. (PROSE: Father Time) Assembled as the Imperial Family, the four surviving Time Lords ruled over all of time and space from the Needle, (PROSE: Father Time, COMIC: Miranda) led by a version of the Doctor (PROSE: The Gallifrey Chronicles) called the Emperor. (PROSE: Father Time, COMIC: Miranda)

The Klade blamed them for draining the universe of energy by starting the War, (COMIC: Miranda) and after several centuries of conflict, the Klade revolted and overthrew the Family. (PROSE: Father Time) However, this did not stop the end of the universe; by the time Miranda Dawkins became Empress of the Needle, there were no stars and the energy drain left everything a dying void. (COMIC: Miranda)

In the time of the Empress, the universe was still a grey void, and all surviving planets were freezing cold. (PROSE: Hope) Entire sections of the universe and its timeline were missing. (PROSE: Father Time)

A boy from Faction Paradox had once told the Eighth Doctor a "Greyness" would fall over reality around the time of the Needle. (PROSE: Unnatural History) The Infinity Doctor saw the Needle was the final structure of life in a grey starless void. (PROSE: The Infinity Doctors)

Council of Eight's History
The Council of Eight were the most successful of the post-War era's new powers in creating their own web of time. Their manipulations took advantage of reality's instability to instigate a multiverse collapse which briefly left the Council's timeline as the only reality in existence. (PROSE: Timeless, Sometime Never...)

Restoration of Gallifrey
After suffering from amnesia for several years, (PROSE: The Burning, et al) the Eighth Doctor realised that, in the last moments before he destroyed Romana III's Gallifrey, he had deleted his memories from his brain and downloaded the Matrix, including the minds of all the Time Lords. Marnal made him promise to restore the Time Lords and build a "city for the saved", and to this end, the Doctor sent K9 to Espero. (PROSE: The Gallifrey Chronicles) There, Madame Xing had previously offered to restore his memories, (PROSE: Halflife) something which the Doctor now realised would cause the Matrix in his mind to be deleted unless he managed to restore it first.

Despite this risk, Marnal believed the Doctor would make good on his vow. (PROSE: The Gallifrey Chronicles) Indeed, the Eighth Doctor had previously glimpsed in the Tomorrow Windows, a possible future in which the Time Lords were restored along with their homeworld. Also among his possible futures, albeit one less certain than the timeline where he became a man with big ears, was a timeline where he was to become a "listless-looking" man; (PROSE: The Tomorrow Windows) this possible version of the Ninth Doctor coexisted with, both of them flying their TARDISes freely and believing the universe to be secure enough that the Doctor even considered retirement. (TV: The Curse of Fatal Death)

According to some accounts, the faction in the War who'd created the Cwejen, the Great Houses, (PROSE: The Book of the War) indeed survived beyond "W-Time" and returned to having great influence over the universe from their Base of Operations. Now calling themselves the Superiors, they inaugurated the new era of V-Time, eliminating their Wartime enemy's lingering influence on reality via a surgical procedure on the regen-inf soldier Chris Cwej. (PROSE: The V Cwejes)

Last of the Time Lords
When the Eighth Doctor looked in the Tomorrow Windows, he saw that his most probable future was to become a Ninth Doctor with big ears and a hawk-like face. (PROSE: The Tomorrow Windows) When this Ninth Doctor met Rose Tyler, he recounted to her how he was the last of his kind following a time war, with the Doctor having been forced to destroy his planet to put an end to said war. (TV: The End of the World, Dalek) The Tenth Doctor continued to consider himself the "last of the Time Lords", recounting to Martha Jones how his planet was gone. (TV: Gridlock)

Although most accounts depicted these events in the Doctor's life as following on from the Last Great Time War against the Daleks, (TV: The Parting of the Ways, The End of Time) with the Doctor's destruction of Gallifrey under discussion having occurred in circumstances involving a weapon called the Moment at a time when Rassilon's High Council were in charge of the Gallifreyan forces, (TV: The Day of the Doctor, The End of Time, PROSE: Doctor Who and the Time War) one account showed that the memory of Gallifrey's destruction at his hand which haunted the Tenth Doctor (PROSE: The Eyeless) was the Eighth Doctor's memory of destroying Romana's Gallifrey. (PROSE: The Gallifrey Chronicles)

Aftermath of the Last Great Time War
Historians who studied the Daleks understood that the Last Great Time War had rewritten the history of the universe such that it was not the same as "the one that had first felt the winds of change". For the surviving Daleks, everything they had ever known was in flux, their past having changed forever. The war had thrown up a bewildering jumble of alternate realities and superfluous time lines, such that no one could tell what had actually happened and what was now fantasy. With the war time locked away from reality, even the events of the conflict itself seemed uncertain. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

Relation to other realities
While numerous accounts indicated the post-War universe and the multiverse based around it was the only reality in existence, (PROSE: Time Zero, Sometime Never..., et al.) this was not necessarily the case.

When exposed to anti-time, the Eighth Doctor of the positive-time universe saw a prime universe where the Time Lords had "ceased to exist, time wound backwards to eliminate their every trace." Additionally, he described seeing a planet Earth where he "plucked out one of [his] own hearts." (AUDIO: Zagreus)

One loa indicated that the War in Heaven timeline had not actually been erased when the Homeworld was destroyed, and that the existence known to the surviving elementals was a result of them "falling from Warring Heaven, crashing to the lesser species" and having their timelines rot into "thorned patchworks of broken memories". (PROSE: The Story So Far...)

Behind the scenes

 * Different writers of the Eighth Doctor novels had different perspectives on how much the universe had changed following the end of the War in Heaven.
 * Peter Anghelides said, "Gallifrey has been wiped from history. You can believe otherwise if you wish – but remember that some people believe the Earth is flat."
 * Lawrence Miles' The Adventuress of Henrietta Street aligns with Anghelides' comments, although as David A. McIntee noted, Adventuress was deliberately written in an unreliable narration style.
 * Jon Blum agreed that Gallifrey had been wiped from history but at the same time remarked that, rather than Gallifrey's unhappening creating a completely new and unrecognisable universe, most things had been unchanged due to Gallifrey's "special relationship" with the rest of time.
 * In contrast, Lance Parkin argued that "Gallifrey didn't unhappen, it just blew up. Some characters in the books think differently, but there's a weight of evidence to suggest they were wrong." Steve Lyons and Chris Howarth's  A Rough Guide was particularly rife with such evidence, as its main premise was that human "temporal tourists" postdating Gallifrey's destruction in The Ancestor Cell began travelling back to earlier eras of Gallifrey's history for leisure, and, indeed, that one of them actually altered the course of a major event in Gallifreyan history.
 * Mark Clapham's Analysis, published in the charity anthology Walking in Eternity, asserted that following The Ancestor Cell the amnesic Eighth Doctor was plagued by dreams of a grey void or nothingness, invoking the "grey universe" seen in The Infinity Doctors and implied in Miranda, Father Time, and Clapham's Hope.
 * Telos Publishing's Time Hunter series, which began in 2003, often mirrored the tone and ideas seen in the BBC Eighth Doctor Adventures and Faction Paradox comics that featured this "Post-War" status quo. Time Hunter frequently portrayed groups or powers attempting to control or conquer time and demonstrated a universe that could be manipulated through magic and rituals.