Here is the scenario I see playing out with ISU landing in the B1G.
UT goes ACC, they could also just park the olympic sports there and go indy for football (not likely) I think this is UTs best pick up if the B12 is going to fail. They can still have some weight to throw around, the SEC and B1G would neuter UT, IMHO.
OU Goes to the SEC - This is a natural fit, it gets OU in a good football conference also helps SEC get a little bit more in Texas, OU is huge in the DFW area.
OSU rides OU coat tails to the SEC - This is a little tougher to me, because OSU doesn't really fit in the SEC, in my mind, but i just don't see OK legislature letting OU run away from OSU.
That leaves 6 teams
KU - B1G fit - This hinges on KU being able to break away from KSU, I don't think the B1G would take KU with KSU.
KSU - Not a B1G fit - With KU in, KSU offers nothing to the B1G.
TCU - Not a B1G fit - Don't see them going to a religious school also DFW is way outside the footprint
TT - Not a BIG fit
WVU - Not a BIG Fit - Could potentially be the other SEC team if OU can get unbuckled from OSU.
ISU - Logical BIG fit, just doesn't move the needle much. But there should be plenty of money to go around. Also as you move away from the Cable/Satellite TV model, ISU lack of population gain becomes less of a concern.
It also works in ISU favor if for some reason, UT or OU decide to take 1 or 3 other teams to the Pac12. This is also when the SEC door may open for ISU, but I think if push came to shove, WVU would get in the SEC before ISU.