There's not a lot of scenarios when you play it all out that look great for BYU. Losing Texas and Oklahoma pretty much destroys the Big 12, regardless of who they pick up.
As much as we want to say a Big 12 with BYU, Houston, Cincy, Boise replacing Texas/Oklahoma is on par with the PAC12, it's just not true. There's no USC or Oregon there with the name/history to be a marquee opponent/recruiter.