I think Sylvanas and the Forsaken would fare better NOT having the spotlight on them after Garrosh is dealt with. I mean, with everyone focused on Garrosh, the Forsaken have been able to do whatever the f... they wanted. She is the lesser of two evils (arguable), and after Garrosh is gone, she will be the only evil left and will come under close scrutiny by virtually everyone.
Or maybe she just wants corpses.