What determines whether the Big 12 would keep P5 status? Wikipedia says that the P5 conferences are designated as "autonomy conferences" by the NCAA. Such conferences appear to have less restrictions on how they can use their financial resources.
Well, not sure who runs that committee, but if the "alliance" conferences have good sway there (and presumably they would) they could certainly ensure themselves of another very loyal and supportive conference by keeping the Big12 as P5...