Everything I can read has said that CA lets you choose between the Vortex and Domination campaign styles. That is, you can play either or.
However, every time I've played and ignored the Vortex, I'm inevitably drawn back into it via warnings that I'll lose the game unless I fight the Vortex Battle (since Mazdamundi has completed the final ritual, or whatever).
So is it really a choice? Or have people completely avoided the Vortex campaign successfully?