It's a good question. http://www.utsandiego.com/news/2012/feb/14/big-questions-sdsu-league-dissolves/
Thats exactly the reason I never got anyones argument that if the Big East "dissolves" because another team or teams leave that nobody would have to pay an exit fee or wait 27 months. It's just not the case. As long as there is a team that doesn't leave, in my mind everyone else pays and adheres to the bylaws. It doesnt matter if it's 1 team leaving or 6. That being said there is always room for negotiations.
Given that the primary reason for dissolving the MWC and CUSA is to break their lousy TV deals, it is ironic and hypocritical that they are enforcing exit fees on SDSU and Boise.