In the military aspect -
In December 1984, Todor Zhivkov began a campaign of forceful assimilation of Bulgaria's Turkish minority, most notably forcing all Turks to take Bulgarian names. By 1989,
resistance to this policy led to riots and terrorists act - bombing of one train near Gara Bunovo, which resulted in multiple deaths.
It can lead to an rissing dissent and revolt risk in the provinces of Smolyan,Tamrash and Ruse.
In May 1989, Zhivkov suddenly granted permission of all Turks to leave the country, which led to over 300 000 emigrating to Turkey within three months.
So there was a real possibility of war between Turkey and Bulgaria in the summer of 1989. It can break as an act of preserving the rights of the turks minority by the turkish side, by an event.
Also by this time bulgarian army was well equiped and have a total strenght of 200 000 men. In case of war with Turkey, there was a plan to destroy simultaneously three big dam on Arda river - in game province of Smolyan which will resulted in destruction of infrastructure in Edirne, Enez and Alexandropuli /Soflu and Oradea/ - the greek side will protest becouse of it.
There was a second plan known as plan "Khan Tervel" which was developed in case of WW3. The bulgarians will receive a nuke from soviets and bomb Istanbul - cutting the bosphorus. In case of WW3 Bulgaria should get claims on turkish and greek part of Thrace.
As for political aspect -
Gorbachev want Jivkov out of power and there is several canditures.
Petar Mladenov - which may serve as gorbatchevist candidature.He was chosen by the bulgarian politburo,so it is a historical.
Andrei Lukanov - which is more liberal and marked orientated.This option can lead to free marked reforms,even some privatization.
General Dobri Dzhurov - which is more conservative than Jivkov but is loyal to Moscow.Also he can lead some kind of military hunta. This option can lead to democratic upraising Romanian style.
Jivkov can ramain in power too.If he remain in power it will lead to some kind of chinese-socialist economic reform.He may withdrow from Warsaw pact and become more West oriented...he even talk with bavarian prime-minister Franz Josef Strauss of the possibility of joining EU in perspective.However this option can lead to democratic upraising Romanian style too.
Other events may include -
In late 1985 Todor Jivkov was invited to Japan and sign economic cooperation treaty with Japan. Jivkov was fascinated with Japans development.
In 1985-1986-1987 Bulgaria buy MiG 29 and MiG 25 airplanes and begin army modernization program.Bulgaria had Scud and SS-23 missiles.
Sending the second bulgarian cosmonaut in space - Aleksandr Aleksandrov - in June 7, 1988
In 1986 the Bulgaria and Greece signed a declaration of good-neighborliness - something like non-aggression pact - based on mutual enmity toward Turkey and toward Yugoslavia. In the begining of 1989 Bulgaria signed a ten-year bilateral economic agreement with Greece.
In January 1989 the Party issued Decree Number 56 - which introduced chinise style capitalism.
Between 1985-1989 Bulgaria has very well developed microcomputers - Pravetz and supply 70% of all electronics in the Eastern Bloc.
In 8 August 1988 Bulgaria start diplomatic relationship with European Economic Community.
At Seul 1988 Summer Olympics, Bulgaria won 10 gold medal and total of 35 medals mainly in athletics and wrestling.
On 8 marth 1988 there was the begining of democracy movement, becouse of the polution of Ruse from romanian heavy industries.- little dissent.
On 10 november 1989 Todor Jivkov resign. And the story of Bulgarian People's Republic end