I sincerely doubt UT is going anywhere. They have constructed their little pond, are raking in more cash than they will get anywhere else (h/t to Miami on that) and they call the shots, with the only need to pay OU just a little deference now and then. No other conference is going to be able to match that scenario in the foreseeable future.
Without UT, P12 expansion is problematic. Expansion can add, but carries a greater risk. UNM, UNLV, UN-R, BYU, Boise, SDSU, potential regional partners, just are not that attractive, and some carry major issues (BYU). You could go into the MTZ to get AFA, CSU, UW, but again, the addition is minimal. It is only when you stretch into the CTZ that attractive partners are there, but UT the whale of the group, is a cancer and too fat and happy to move, so you wold be picking up the schools that want a life raft from the wake of Bevo.
I don't think any P5 conference stretches over 3 TZ's. TV slots would be difficult. I think that is why nobody else does it. The ACC, SEC and BInteger get the early and early afternoon slots, B12, BigINteger and P12 get the early afternoon, P12 and the elites fill the late afternoon and evening spots.
Right now, the P12 is probably better off standing pat. The lack of population concentration in the west is the problem. There just aren't enough schools/TV sets to make it worthwhile.
If and when the B12 expands, they will not go into the MTZ for the reasons above, IMO.