I don’t think that Sylvanas knows about the “secret baby” or that she started this war to draw out Bolvar, who, by the way, sits in his citadel practically alone. If she wanted to, she could have led the entirety of the Horde over there to kick that glorified babysitter’s ass.
I do think that he would play a part in future though, but I doubt that he would ever take a clear side of one faction again. He is allied with the Ebon Blade for now.