My guess is that the SEC and Big 10 take maybe 4 schools currently in the ACC, and maintain their position of power and financial top level status. The Big 12 and remaining ACC merge into something. Perhaps the ACC schools that aren't really that committed to big time college athletics (BC, Wake) drop down a level to like an AAC or whatever.
A playoff that's majority SEC and Big 10 with a handful of spots for the next tier and maybe 1 of the current G5 results in this aftermath. This gives the Big 10 and SEC all the power and money they want, with enough access to everyone to prevent anti-trust suits.
Within the Big 10 and SEC, there will be a re-arranging of finances. The Purdues and Rutgers of the world won't be culled per se, but they'll no longer be paid as much as Ohio State and Michigan. They'll be given the choice of being paid to associate with those schools and take losses, or attempt a more competitive but less lucrative existence in the BigACC or whatever that entity goes by.
The tiers that are obvious today will become more cemented in a de facto sense, but probably not formally.