Borusa's final High Council

Lord President Borusa's final High Council was the administration that dealt with the crisis that later became known as the Death Zone affair. (PROSE: The Eight Doctors) High Chancellor Flavia and Castellan Jerricho composed the Inner Council. (TV: The Five Doctors, PROSE: A Brief History of Time Lords)

Origins
Borusa's last Inner Council was far smaller in size than that of his first High Council. Firstly, Councillor Hedin had been killed during the Second Omega Crisis. (TV: Arc of Infinity)

When the Death Zone was reactivated, (TV: The Five Doctors) Chancellor Thalia and Cardinal Zorac were sent to investigate by Borusa, where they both perished, (PROSE: A Brief History of Time Lords) from being struck by bursts of psychic energy converted into elemental weaponry fired by Rassilon from the astral plane of the Matrix. (PROSE: The Legacy of Gallifrey)

A Gallifreyan historian identified Thalia and her replacement, Flavia, as being part of different administrations. (PROSE: A Brief History of Time Lords)

Term in office
During the Death Zone affair, Flavia and Jerricho overruled Borusa so that they could employ to rescue the Doctor, who had entered the Death Zone, rewarding him with a new regeneration cycle should he suceed. Later, Jerricho was shot and killed by a Commander of the Chancellery Guard when trying to escape his custody after being framed by Borusa for engineering the crisis, who had planted covincing copies of the Black Scrolls of Rassilon in his room.

Ultimately, Borusa was uncovered as a traitor seeking to become President Eternal. He accepted Rassilon's offer of immortality by claiming the Ring of Rassilon. Like all the others who had sought immortality before him over the years, Borusa was trapped as a living statue and remained in the Dark Tower after the games were shut down again.

As Flavia put it to the Fifth Doctor, this essentially disqualified Borusa from the presidency, ending his tenure. (TV: The Five Doctors)

Aftermath
With a gap left at the very summit of Time Lord hierachy, the Full Council excerised its emergency powers to appoint the Fifth Doctor as the new Lord President to take office immediately. However, the Doctor left Gallifrey to continue his travels with Tegan Jovanka and Vislor Turlough, appointing Chancellor Flavia either as Acting President (PROSE: The Eight Doctors) or Deputy President. (PROSE: The Five Doctors)

Although Borusa was officially declared missing after the events of the Death Zone in order to preserve the High Council's reputation, they were soon forced to acknowledge that Borusa had caused far more problems than the obvious. Certain of his impending immortality and responsibility to be Gallifrey's true ruler, Borusa had not only discredited and dismissed many of the more competent Time Lords from the High Council but had also created a council composed of weak-willed Time Lords who lacked the personal strength to take action without him. Faced with a political system on the brink of collapse, the Time Lords were forced to recall the Doctor to act as President, as he was a relative outsider with no ties to anyone else who would be controversial enough to establish himself as a credible candidate. (AUDIO: Time in Office)

Borusa briefly returned to lead Gallifrey in a period known as the Borusa Interregnum, during which President Niroc's High Council was ousted and new elections were held. This time was recorded in the Secret Scrolls of Rassilon, eventually becoming known as a legend. (PROSE: The Eight Doctors) Tales of Borusa serving Rassilon during the Last Great Time War (PROSE: Engines of War) had also become legends by the time of one historian's native era. (PROSE: A Brief History of Time Lords)