If they quit the bevo10, then the SEC wont have to 'raid' anyone. they could simply invite aTm, then announce that 1 or 2 more spots is open for the bidding.
That was the SEC's announced process (e.g. no raiding other conferences and being exposed to potential litigation).
If aTm goes knocking at the SEC door and is told to buzz off it could get interesting.
The expectation is that aTm will be admitted. Some other school will have to announce their departure as well. I have a hard time believing that there will be 14 in the SEC starting next season. 2013 is much more plausible.