According to various reports, the SEC is content with the status of the conference and has not invited the Texas A&M Aggies into the conference, despite rampant Saturday internet grumblings.
The Texas A&M Board of Regents is planning on meeting this morning to discuss the future of A&M athletics in the Big 12, and explore the possibility of moving to a new conference. The A&M Board of Regents will likely vote on switching conference, claiming that the Big 12 is unstable and could crumble at a moment's notice. This vote will likely pass.
According to I Am The 12th Man, after the vote, the Aggies will apply for admission to all other BCS conferences, thus evading any legal argument that the SEC and A&M colluded in any way to form the bond.
After that, keeping in mind that the SEC did not shut the door on expansion, I would guess the SEC would reconvene and vote specifically on admitting A&M into the conference. The vote by SEC university presidents wasn't specific to A&M, since A&M hadn't formally applied to the conference, and could be seen as a shield against legal action by the Big 12 conference.
I can't imagine the SEC inviting A&M into the mix alone. They'd need a minimum of one other schools, with a possibility of three other schools to apply, be admitted and start in the conference during the same year. This might not be until 2013 or 2014, depending on the contracts the other schools have with their current conferences.
Needless to say, unless something drastic happens, A&M's plan to be in the SEC for the start of the 2012-13 school year might be on hold for now, but the viability of the Big 12 is certainly in question.