She doesn't have to die but I can't see her being Warchief much longer. I could very easily see her turned in to the Horde's version of Illidan and Nathanos would take her place as leader of the Forsaken (he did get a fancy new model)
I just think she has far too much going against her to stay in power. Genn, Jaina and Anduin all want her gone. If Vereesa dies you can add Alleria to that list as well as Turalyon, Arator and the entire Silver Covenant. Tyrande will probably be on that list after Teldrassil. Vol'jin is returning and we know he's never liked her and I think his plan to make her Warchief was to basically put the spotlight on her and force the Horde to deal with her. I'm hearing that Saurfang may also have a potential beef with her. While there is no evidence that Saurfang and Baine actually want her gone we do know they don't like Gallywix and Sylvanas is working very closely with him right now. Thrall is supposed to be getting a pretty big role in Battle For Azeroth and something tells me the expansion is going to end with him as Warchief again. I think Vol'jin will convince Thrall. Besides, I can't see Thrall being too happy with what Sylvanas has done to the Horde that he founded. I dunno, I just think there is far too much going against her for her to still be Warchief at the end of the expansion.
As I said, I'm not saying she has to die but I don't see her leading The Horde and maybe not even leading The Forsaken. She could just be turned in to a important neutral NPC such as Khadgar, Illidan, Magni, etc
....Either that or she kills Bolvar and becomes the Lich Queen. Who knows with Blizzard.