It's been done before. http://www.redorbit.com/news/general/10239/four_big_east_schools_sue_miami_acc
didn't stop them from leaving though.
But that assumes the SEC didn't throw this contingency out there to save face because they don't like subsequent expansion candidates.
I agree with you, if this true, and the SEC will actually say no if someone doesn't simply waive the right to sue, it means the SEC's lawyers think they may have done something to put themselves at risk, or they are looking for a way out with limited liability. A&M stuck their neck out there pretty far...it would be pretty embarrassing for the SEC to say, "Well, I can't get a decent ACC school to join with you, so you may want to see if you can go elsewhere."
Either way, this is more significant than what Billy Liucci is trying to blow off.