I don't think there is any way Boise State can go back to the Mountain West now.They'll find some way to keep the WAC alive and put their Olympic sports there or they will in conjunction with the Big East exert enough pressure on the Big West to allow them in.
The bottom line is that in June of 2010 Boise left the WAC because it was a crappy football league. Now the current Mountain West is like the old WAC with a few MWC hold overs who could not get invited to the big table. At least the Big Least has Louisville, Rutgers, Cincy, and now SMU, UCF, and Houston. It is not great but still better than the Mountain West.
Boise State is just posturing in my opinion. They will be in the Big East in 2013.