The numbers I have seen thrown around to leave now are in excess of $100 million for standard ACC teams. but here is the kicker. ND is not in the ACC for football, but are for all other sports, and let's face it, they will be and are target #1 for the B1G now.
They can afford to leave based on just their olympic sports and the penalty they would incur for pulling them out of the ACC, but their leaving would also void their 5 game a year deal in football, opening up the TV contract and more importantly, the GOR for renegotiation.
I honestly believe that will be your path out and whoever else can latch on. And I think it will come soon.