Well, when you've gone so far as to try and kill Thrall, there's really no turning back.
That's assuming she's not all purposely setting this up. For now she isn't exactly treating this rebellion like an existential threat. How deep that plan goes, is anyone's guess. Honestly it could be quite shallow: Trying to get all who would oppose her reign in one place, then kill em off.
Whatever happens. I doubt Vol'jin figuring out who put her on the throne will help. Even if that all works out, Sylvanas and the Horde learn important lessons and team up. And it all turns out to work out for the greater good of the Horde. Even if Sylvanas were to step down. It would not make a satisfying story for the Alliance. And unfortunately, the game is bound by its structure to have to at least pay lip service to both sides.
Especially cause it's likely that the ultimate victory this expansion has to largely belong to the Alliance. Sylvanas is their antagonist, after all.