So the PAC-12 have decided not to expand, thus largely leaving Oklahoma, Oklahoma State, and Texas Tech in the Big-12. That still leaves 2 thorny issues and 2 uncertainties.
The two thorny issues are conference revenue sharing agreements, equal or unequal. If the conference is to regain stability, rather than going through this drama and turmoil again, it will need to move to equal conference revenue sharing. Doing so will facilitate the conference members to act as a team rather than continuing on every school for itself. Which brings to bear the next thorny issue, which is the Long Horn Network (LHN), U of Texas and ESPN 300 million dollars 10 year partnership sport channel. The LHN, and UT's attitude regarding it, was the essential reason why Texas A&M left, this is the primary reason why the PAC-12 decision against expanding to 16 with OU, OSU, TTU, and UT. If UT and the LHN cannot or will not become compliant to the Big-12 expectations, then UT should not be a football member of the Big-12. UT will be fine as a football independent and should not have a problem scheduling annual games with OU, TA&M, TTU or any other regional teams. UT would have no problems arranging for games with USC, UCLA, Stanford, or Notre Dame. In many ways both UT and the Big-12 would both be better off with an independent UT.
The other uncertainty is Texas A&M (the first is whether UT should go independent or not). If revenue sharing and UT/LHN will comply with the conference, then TA&M may decide to stay. IF UT is independent then TA&M will likely stay in the Big-12.
Once the thorns and uncertainties are clarified, the Big-12 should expand to at least 12, if not 14 or even 16. With either UT or TA&M the next three teams the Big-12 needs to get back to 12, and thus host a conference championship game, would be to add BYU, TCU, and Boise State. All these are competitive teams with national standings. I believe though stopping at 12 would be a mistake and the conference should go to 14 with the addition of Air Force or Colorado State (for the Colorado market) and Tulane (for the Louisiana/New Orleans market). I think 14 would still permit two divisions with a reasonable conference schedule of 9-10 games (6 divisions games, 1 cross division annual rivalry, and 2-3 rotating games from the other division). To go to 16 would mean a pod based arrangement with 4 teams each, 9 conference games. But other than Colorado State/Air Force who else? Wyoming? New Mexico? A 15 team conference would means 3 pods of 5 (4 intra-pod games, 2 inter-pods annuals, 4 rotating intra-pods. Expansion to 14 I think would be reasonable for now rather than going to 15 or 16 to be a super conference.