Followed by the unexpected end of your employment at Blizzard I imagine as their monthly revenue stream drops to zero.
WoW2 is never going to happen as a separate launchable product. It will just gradually creep into the current game over patches. So Warcraft IV, clearly. Blizzard is developing a brand new engine for their Titan project. If I were in charge of a company doing such a thing I'd probably mention at one of the early design meetings to leave enough hooks in it so that my other MMO with its ancient engine could be ported to it someday. But that's probably just me.
It's fine and all to think about how things could go in the future but positing things that are vanishingly unlikely to ever happen is a waste of time.
Although I'll leave a caution about a Warcraft IV: People endlessly fantasized for years and years about a Diablo III. So be careful what you wish for. It might be better to leave things where they are to be honest.