But the question is how many people will end up buying Wrath post-Warhammer launch?

I know I won't, and I know a bunch of others who also won't.

So they could end up looking at much lower sales numbers, because of more competition and people just being tired of the main problems with WoW not being fixed.

Hopefully all the flaws with WoW are addressed in Blizzard's next MMO. I can't see them just trying to release the same old thing like many Korean companies do.