Sacred Haven of Debauchery

I've always wondered why many consider the Empire to be evil and the Republic to be good. With a single ruler, there won't be any conflicts, is that evil?

Probably because any dissent is suppressed at the root, right? I think that's why empires are disliked. In Russia, for example, there is dissent, but it takes distorted forms and doesn't affect anything.

And also, let's say the Emperor and Vader died, what happens next? This doesn't mean that the Republic will win.

The Emperor has no heirs. Except for Vader. And Vader doesn't have any either :) No one to take the reins :) And if the Empire is truly disliked, then these conditions are enough for most of the planets to leave its composition and join the New Republic. Although fanatics and troops will remain in the Empire, yes.