I think there's very little chance UNC would accept. UNC is in good position for an invite to Big Ten or SEC, certainly not because of football and not even so much because of basketball, but because both conferences want a foothold in North Carolina (and Virginia).
Specific to ACC, here's how I think realignment plays out, albeit not until after the GoR expires:
Clemson, Florida State, NC State and Va Tech to SEC;
UNC, UVa, Miami (probably) and Georgia Tech (possibly) to Big Ten.
Big XII will pick up some of the leftovers. Miami and/or Georgia Tech, definitely, if either or both get passed over by the Big Ten. Probably Pitt and Louisville, in a "we put the band back together" sort of move, given that each has a natural rivalry with an existing Big XII member (WVU for Pitt, Cincinnati for Louisville.) Probably Duke and Syracuse for basketball. I think Fredo and Wake are up the creek without a paddle. UConn (for basketball), South Florida (travel partner for UCF) and Tulane (somewhat natural fit within Big XII existing footprint, yet outside current footprint) all probably have a better chance of a Big XII invite than either of them has.
...is if the ACC falls apart such that the Grant of Rights, which has been the sticky wicket in all this for the ACC, is no longer applicable.
In that event, ND likely would end up joining the B1G.
Date. As I understand it, any modification requires unanimous agreement. I also happen to think there is zero chance that it gets extended, as the unanimity requirement cuts both ways.
As for the possibility of leaving early, consider that Oklahoma and Texas had to pay about $100 million (not sure if that figure is combined or apiece) to get out of the Big XII's GoR just one year early. Since ND football is a separate entity, ND likely wouldn't have to pay that much, at least not proportionally, but it still could get pretty expensive.
If ND became a free agent so to speak would the B1G really kill a deal that could get ND in for football because they'd want every sport? I don't know enough about how the Big East would be able to accommodate other sports this is just more a dream about what would be the perfect hoops conference for ND in my own mind.
I don't think BE schools are going to have the money to pay enough higher end talent and coaches to remain successful.
If the B1G were willing to have ND in the conference except for football at virtually any point in time, I think it would have happened already. And I see the changing landscape of conference realignment as making it much, much less likely that the B1G (or any conference who hopes to continue to have access to D1A football playoffs) taking ND except football.
Could ND rejoin the Big East? Sure, but the other sports just don't line up that well with the Big East.
I personally think ND will belong the the B1G in all sports in the next 10 years, including football. Note that I think that will happen, that's not what I want to happen. Also note that this assumes that the ACC's Grant of Rights dissolves (or is close enough to make the exit money tolerable).
join
And ND would want their sports in the B1G.
He will be the white knight to broker the future of high level college athletics. I would not be the least bit surprised if he is already involved at some level in planning. The question is would his loyalties to ND hold up in brokering a deal or would he sell out ND if the price is right.