There do not appear to be any "legal" arguments as to the damages: (1) the contractual issues between the conferences have been waived by the b12 (the B12 and the SEC are contracting parties under the BCS); (2) A&M exited the B12 through proper contractual avenues; (3) the individual B12 schools lack any contract privity with respect to the SEC; and (4) from the facts I've heard, there is no chance at a tortuous interference with contract issue against the SEC: so there aren't really any "legal" issues to sue on.
There are, however, so-called "equitable" issues that the B12 individual schools can sue on: namely, "reasonable reliance." You may have noticed that phrase "reasonable reliance" in a number of press releases and statements relevant to the Baylor issue. This is a weak, yet plausible, theory of recovery.
The reasonable reliance theory would basically allege that either A&M or the SEC had given the individual schools (possibly through the B12 conference) assurances that: (1) either A&M would stay committed to the B12 or (2) the SEC would not admit a B12 member. If this nonsense ever got to court (which it wouldn't), the main issues would be whether the SEC or A&M gave such assurances, and if so, whether the individual B12 schools "reasonably" relied on those assurances.
Unless the assurances in question were concrete promises, the reasonable reliance theory is almost certain to fail, because as others have pointed out, the Nebraska and Colorado exodus gave notice to all B12 schools that further departures were foreseeable. Therefore, Baylor would be hard pressed to argue that it spent millions of dollars towards future B12 seasons in reasonable reliance on A&M staying in the B12, if A&M had refrained from making any concrete promises.
The big factual question is, after Nebraska and Colorado left, did A&M make a stupidly concrete commitment to the B12? I cannot imagine that they did. That would be the only way that a reasonable reliance theory would hold water.
Anywho, much ado about nothing. I applaud Baylor and the B12 leftovers for putting up a fight, and to their credit they have bought themselves some time.