The Doctor (Alien Bodies)

The final incarnation of the Doctor died during the War in Heaven. His corpse became the Relic. (PROSE: Alien Bodies)

Last adventures
Throughout the Doctor's adventures, he accumulated much knowledge and experience that was codified in his biodata, including the biodata codes of assorted Time Lord presidents. The Doctor's final incarnation claimed to the Celestis that he knew the codes used to build Mictlan and could destroy it at wish, though Kristopher Patrick Englund believed he was bluffing. (PROSE: Alien Bodies)

Two days before the first battle of the War in Heaven, one of the more interventionist and optimistic members of the Great Houses visited Dronid, claiming he had an old connection to one of the enemy's agents there. However, his diplomatic attempt apparently failed, and he was believed to have died as the battle started. (PROSE: The Book of the War)

However, Qixotl was involved in the true story of the Doctor's death, which was much more complicated. Even after the fighting on Dronid had already begun, a dying soldier was visited by the Doctor on Simia KK98; at that time, the Doctor said that he was just observing the conflict, that he wasn't working for the High Council, and that he was only one of the enemy "depend[ing on] where you stand." (PROSE: Alien Bodies) When asked who the enemy was, Abschrift replied, "Who indeed." (PROSE: Warlords of Utopia)

Right before the Cataclysm, the Doctor's TARDIS materialised in the Grand Hall of Mictlan. The last incarnation of the Doctor told the Celestis that he wouldn't let them involve themselves in the affairs on Dronid, and they agreed to remain neutral if he gave them his corpse. He accepted these terms, but only if they freed some of their servants and satisfied one other stipulation.

After being captured into Marie's interior dimensions, the Eighth Doctor had a premonition of his future self's confrontation with the Celestis. During the premonition, he said that he had been a slave; the Eighth Doctor wasn't sure why he said this. (PROSE: Alien Bodies)

After death
After eventually dying, the Doctor's corpse became known as "the Relic" and was planted in a bunker under the ruins of the city centre of Smithmanstown on Dronid. Since much of the information in the Doctor's biodata had been lost during the War in Heaven, his body was very valuable to many Wartime powers, including the Time Lords, their enemy, Faction Paradox, the Celestis, UNISYC, and the Daleks.

Since most psychics retained some power even after death, proportional to their powers while alive, the Relic generated a psychic "call" particularly attuned to nearby humans. During Qixotl's auction for the Relic in the Unthinkable City, Colonel Kortez had an out-of-body experience while meditating, and on "Cloud Seven" he met the Doctor, who appeared taller and older than Kortez remembered, wearing a shroud over his head so that his facial features were indiscernable. (PROSE: Alien Bodies) "'We are all of us living inside the bottle,' the Doctor explained, while the worms of the astral plane began eating away his flesh. 'And one day, the bottle will break. Then all worlds will be one world. The inside will meet the outside.'"

- Kortez's vision

Christine Summerfield had a memory of playing with a Ouija board with some friends in Lady Diamond's shop, and the resultant message included the sentence, "We are all in the bottle and one day the bottle will break." (PROSE: Dead Romance)

After the Eighth Doctor tricked the Celestis into giving him the Relic, he took it in his TARDIS to Quiescia, where he destroyed it with a thermosystron bomb. (PROSE: Alien Bodies)

Behind the scenes

 * PROSE: The Book of the War states that this future Doctor was a "particularly interventionist" diplomat on the Homeworld. Given the suggestions in that book and PROSE: The Taking of Planet 5 that the War King is the Magistrate, this lines up with the idea that this Doctor is the incarnation from PROSE: The Infinity Doctors.