It is hard to say, but you can expect people who buy Halo Wars thinking it is a FPS and come home and see small armies getting blown to bits while trying to place a well timed counterattack.
Halo is identified with the FPS mode, nothing else. I can see the casual market returning this game because they thought it was a FPS.
Halo ODST is another story though.
I have to say KZ 2 will sell more.