Texas does NOT need the rest of the Big 12, it is as simple as that. They have little competition in the Big 12 other than Oklahoma.
If Texas A&M moves to the SEC, THAT scenario changes the scene for Texas. Even WITH their contract, what would fans (other than Texas fans) want to watch---games with the clowns, KSU, Kan, and Misourri or games Texas A&M plays against SEC teams like Alabama, LSU, Arkansas, Florida, and so on?
Plus the last thing that Texas WANTS is have the SEC move into the state of Texas. That conference has a lot of money and power to throw around.
And if things don't quite work as well as Texas wants, they will just become an independent or join the Pac10 or SEC (or maybe even the Big 10) and everyone else in the league can jump into the ocean.
If Texas A&M flys, that leaves the Big 12 conference wide open. A major player would be leaving. The rest of the conference would crumble...Oklahoma would quickly look to go elsewhere. That would truly be the end of the Pac12 conference.
In a major realignment, perhaps the Big 10 could persuade Texas and ND to join? Saying that, I don't want either in the league.