I don't think MU, CU, Neb or A&M would return to the B12. I think the move was a clear win for CU in almost every way. Nebraska won't leave. It would be unprecedented for the B10 to boot them, and that's the only way they would leave. MU and A&M might have some motivations to leave the SEC (like A&M to flip the bird to Texas one more time), but there is no better financial situation for them anywhere, so that idea is just a muse.
I don't see many of the current/new B12 schools as targets for a power4 conference with the exception of KU and WVU (and maybe ISU). A case could be made that these two (or three) fit naturally into a P4 conference geographically, culturally and/or academically. The ones that just moved up to the B12 are not going to get a whiff at the P4. The remainders (OSU, KSU, TT, TCU, Baylor) don't have a chair in the P4.
If I had to guess, here's what I think will happen (BTW, I haven't really been right about how any of this has actually gone down, so this probably won't be reality, but hey, it's fun to speculate!):
First, KU will sit tight and let the new B12 stabilize. For the next couple years, despite the weak football program, KU will have an opportunity to be the esteemed leader of the conference. A few years later, when the TV contracts come up for renewal, KU (and maybe one or two others) should have an opportunity explore a possible exit. Depending on how lucrative the contract is for the new B12, KU will have to decide whether to be a big fish in a little pond, or move to and become a little fish in a big (but more stable and more lucrative) pond. If KU leaves (and I think they should if they can), at least some of the remaining B12 will merge with the Mountain West, which has 11 members right now.
With all of that transition, the B12/MountainWest will lose its status as a power conference. Nearly all of the P4 conferences will have 16 teams and can easily form a balanced elite college league and milk a huge contract for their conference and league playoff championships.
The music will have stopped at that point. There will be those on the inside and those on the outside and homeostasis will be reached.