We should kill them both as far as I'm concerned.
Sylvanas is completely overrated. She's died three times, had her ass handed to her an additional three times, and relies on nothing short of divine blizzard intervention to win anything. "Oh you killed the val'kyr attacking andorhol? Just kidding! I have more, and we win!" And I
Still have no idea why the worgen had to abandon gilneas after personally kicking sylvanas around and sending her running with her tail between her legs.