I did leave out two important facts:
1) Since Boise is staying in the MTN SDSU has a clause in their contract with the Big East that if Boise were to leave, SDSU's exit fee would be waived.
2) SDSU has until 1/31 to decide if they want to stay in the MTN before the MTN can offer any other school.
This article breaks it down: http://espn.go.com/college-sports/story/_/id/8803804/mountain-west-conference-give-san-diego-state-aztecs-first-option-join