Short answer: Oligarchic Republic → Republican Dictatorship → Feudal Monarchy ( < 50 republic tradition) or Oligarchic Republic (>= 50 republic tradition) or Constitutional Republic with rebels
Long answer: Without events that decreases republic tradition, and death of counsel, it will take about 17 continuous reelection to drain all of the republic traditions to 0. The reelection every four year will -10 republic tradition each time, and the republic tradition recovers one every year in normal stances. If -6 republic tradition in every four years, then it should take 17 time to lose all 100 republic tradition.
In another word, without events, it will take 17 X 4 = 68 years for the counsel to drain all republic tradition. This doesn’t include if the counsel died in mid game and forced to hold a premature election.
Republican Dictatorship (Require Res Republica)
By the time when the republican tradition is zero, the government will switch into Republican Dictatorship. You will have that old, awesome re-elected multiple times counsel as ruler until his death. In the same time, the republic tradition will stay in 0 and will not recover unless events are triggered. The side effect of +200% on raising stability will stay until the dictator dies.
Although it is a dictatorship, the nation cannot have royal marriage and won’t have heir. I used console command to give my dictator an heir but it doesn’t matter to the court. Nevertheless, even the republic became a monarchy in the end, the plutocratic ideas group will still exist if being chosen. Hence it is possible to have both plutocratic and aristocratic idea groups in the same time. (But who takes the aristocratic idea group anyway?)
Saving the Republics (Require Res Republica)
Of course, there are ways to turn back to Republics, or even going to a better republic. As mentioned earlier, we still can rely on events to gain back republican traditions. If there there are 50 or more republican tradition when the dictator dies, the government will become back to Oligarchic Republic. If the republican tradition is below 50, then it will be a Feudal Monarchy. Nevertheless, there’s a republican dictator event that spawn rebels and those rebels can switch the government into Constitutional Republic.
No dictator is being harmed when writing this blog and researching this government shift.