The NBC contract means next to nothing. If ND is ready to make the final step, then ND will either make it with NBC being cooperative, which will be necessary for NBC to maintain any relationship with ND or any ACC schools, or else ND and the ACC will deal with it. There are several ways it can be dealt with. My guess isa that NBC would want to be to the ACC what CBS is to the SEC - that NBC would want to have rights to show 1 ACC game per week. To get ND on board fully with ESPN, ESPN would go along with that, as long as NBC were restricted from showing ND to maybe 4 games.
I think you are missing the key point about Navy. If ND is now in talks about when it will go full member in football, Navy will be part of the talk, as will divisions (assuming the NCAA stops brown nosing the Big Ten and allows an end to divisions). ND will not make the move unless ND is in a division that makes sense for ND. For example, ND has played Pitt far more than any ACC school. If ND is told it can't play Pitt annually, ND will be offended, and rightly so.
The indispensable fact is that ND has played Navy in football more than ND has played anybody. Navy is ND's most played rival. That matters, a great deal. So, you can count on ND saying that its cost to join is to have Navy as #16 and divisions that make sense for ND football.
But ND is not stupid. And ND knows that some schools are so valuable that you do not back away from them, that in fact you pursue. ND people know that if Texas and ND are ACC divisional rivals, the Irish-Longhorns game will become as big as any in the country from year one of the league rivalry. As I say above, Texas has no obviously best path. Every move Texas makes, including keeping its Big 12 ten member status quo, is risky. And I think the best long term move Texas can make is to the ACC providing it is paired with ND. Thus, I have little doubt that ND and Texas people have discussed that very thing, just as ND people and ACC-office people have discussed it.
If ND is ready to play for the ACC football championship and Texas decides to sink with the Big 12 and Navy decides to stay AAC, then I think the school most likely to get the offer is Cincy. Morgantown, WV is 70 miles from Pittsburgh. Adding WVU would be 0 help to an ACC network, and WV produces no players, in either revenue sport. The Cincinnati TV market (only the 3rd largest in OH) produces far more talent in both revenue sports than does WV. And perhaps the coup de grace - ND has 0 desire to play in Morgantown but is happy to play in Cincinnati.