I doubt Texas leaves the Big 12, but if they do, it would be for the SEC. The PAC 12 has no schools that really interest them, whereas Nebraska, Texas A&M, Arkansas, and Missouri, all former conference mates, are in the SEC. OU would probably go with them and take OSU.

Texas likes being the big fish in the Big 12, so moving to the PAC-12 or SEC would mean a loss of status for them. Indy is for programs that can't get into a conference these days.