Possible outcomes:
1. Grand Alliance
They all go to 16 and face down SEC/ESPN together. These 3 of the P4 are the face of academics, student athletes, tradition, mom and apple pie (true or not, that would be the marketing pitch).
ACC takes WV
B1G takes KU & ISU
Pac12 takes OSU, KSU, Tech, and TCU
2. Non-Aggression Pact
They won't raid each other, but not going to necessarily help each other out. Pac expands to 16 (maybe 20), but ACC and B1G hold pat.
Pac12 takes ISU, OSU, KU, and Tech
3. Fake Alliance Doublecross
This is where we get a P2 superleague setup. B1G raids some Pac12, maybe even makes a play at some ACC teams and GOR be damned. ACC loses some teams to the SEC as well. SEC and B1G end up at 20 teams each, and what's left of the ACC, Big12, and Pac12 end up being 2nd tier college football.
ISU would end up in 2nd tier. You would probably have four 10 team leagues here, kind of west, southwest, midwest, and east.
None of this is going to happen any sooner than next year, and maybe a year or two after that.
I would guess that #2 is most likely situation.