We'll have to see personally I think Sylvanas getting killed by the Alliance would make a lot of sense it would be devastating and out of the Horde's hands. I think the factions will always remain a thing as we love our Alliance and our Horde.
I've never really seen the Horde as "villains" except maybe in Battle for Azeroth when under Sylvanas but when under Garrosh it was clear his Horde were baddies & most of the Horde rejected it so for the moment? Yeah the Horde are antagonists to the Alliance but that can change.