If you mean The empire in SWTOR only lasted few years in war and then you are wrong they survived a war against the republic and both sides was forced to have peace. and they managed to survive in the real world outside the shadows for 200 years if I'm correct? It was the Emperors Greedy way of trying to destroy his own empire together with the Republic just to become more powerfull and live alot longer than he already have.
Another thing that destroyed the empire was there inner conflicts and power plays. If the Emperor have steped up atleast there and killed the reasons of the conflicts the Empire would think twice befor stating a inner conflict again.
They did probebly have the strongest being in the History of the galaxy and the striongestthat have ever lived as there leader. The way he got weaker befor the fight makes no sense as they discribe it in the game *** do the action from stoping few bombs for exploding weaken him? :/ If the Empereor had come into the open more often the Sith Empire would defenetly rule the Galactic Republic and do far more let them rebel in the end the rebels will lose as they arent as strong and well armed as the republic was.
So I belive a little change should have been made and it would be perfect