There is a grant of rights agreement that says the conference owns broadcast rights to the games of any team that leaves during the term of its TV contracts, and those contracts were extended recently. What conference will want Texas without the right to broadcast its home games for the next decade?
It seems more likely that the Big 12 will add teams. BYU and Colorado State are possibilities, but they might want to look towards the east for a team in West Virginia's part of the country. I'm sure Cincinnati would pounce on the opportunity, but who really wants Cincinnati?