My imagined scenario is so entirely different from the one I see repeated here. The GoR is not just some pinky-promise that can be discarded on a whim. There are financial consequences. And when one team, say Oklahoma, decides to leave the conference, the other teams are not going to scatter and abandon the GoR themselves. They are going to embrace the GoR and use it to bludgeon Oklahoma into painful poverty. They may privately try to find a new homes while they dismember Oklahoma, but they will not make that public. I would speculate that some of the less attractive programs may have already developed a plan to reorganize and grow the Big 12 in the event of a departure of OK, TX, KS.
So Ok has only their Tier 3 rights when they arrive in the new conference. They will not get a share of the Tier 1&2 money from either conference. If it's B1G or SEC, their cable channel money will be fractional for several years. Now, Oklahoma is a rich program, that can maybe survive that kind of hardship for the next ten years.... maybe. But next comes the damages from the individual schools. What if OK's departure invalidates the Tier 1-2 contracts, or greatly dimishes the payout. Each of the remaining schools will attempt to hold OK liable for their revenue loss. This is why composition clauses are so critical. The Big 12 will not collapse and the GoR will not disappear until the nine jilted schools take their pound of flesh.