Three teams leaving the ACC is not nearly enough to cause it to implode. You need 8 or in some accounts 10 teams leaving the conference all at the same time to have the votes to disband the ACC. ND was foolish and did not ask for or get a clause that stated WHO or how many teams had to be in the ACC for their contract to be valid, and as long as the 4 core teams are still there, UNC, NCSt, Duke, and Wake you would have a VERY hard time in court saying that the remaining 13 teams plus whoever is added is not functionally the same conference or so similar as to make the contract still valid.
I agree the ACC is a powder keg, but its one with a very long slow burning fuse. Pitt, Wake, UL, BC and the other low appeal schools in the ACC will NEVER let the big names out of the contract, and there just are not enough spots in the SEC and BT to give enough homes to enough of the schools in the ACC to garner the votes to cancel the conference. IF ND could have found any way out, they would already be in the BT..... same with FSU, Clemson, and Miami into the SEC. As it stands those schools may be WANTING to get out, begging for a release, and privately fuming about their situation, but there are not enough lawyers, guns and money to make Wake Forest to vote itself out of P5 athletics; and that is where it stands.
ND's situation is even worse, even if the GOR was cancelled tomorrow, they still could not join any conference BUT The ACC per their contract.....their only way out seems to be to go all the way in, fulfill that portion of their contract, and then wait for the GOR to expire and leave when FSU, Clemson, and Miami do.