1. I wouldn't be interested in a Universe where the Sith Empire (erected by Darth Sidious) would rule, with Luke and Leia dead or dark.
Also, I wouldn't be interested in a Galaxy where Thrawn has won: I couldn't imagine anything interesting from that outcome. Anything that would appeal to me.
2. About Roleplaying:In Roleplaying there are ALWAYS small bands of people experiencing "Adventures" - and thus often saving the world ! It's almost a Tradition.
When - in RPG - a evil character finally wins, the whole band of adventurers would be dead - at least that's what I expect - and the "Adventure" would be over.
A wholly different approach would be to erect a RPG System where *everyone* should be evil, and battling against good ones - exactly the other way round than normally known.
Finally I say that it is simply part of my nature to let the good ones win : I woulödn't want to live in a world controlled by evil ones (remember ! : the Jedi died out ! Luke was the last remaining fragment of this whole group !).