They wait. If the ACC folds (and you know FSU, Clemson want out, and UNC, ND, UVA would bolt if it folds), the PAC would
Prefer ACC leftovers over any of the existing options out there. And if the ACC does fold, you might have two that go to the SEC, two that go to the B1G, and 4-6 to the B12. There would be some - Stanford, Cal, etc - happy to go to the PAC.