The ACC needs Notre Dame more than Notre Dame needs the ACC. Even looking at Miami - if they hadn't beaten Notre Dame and instead beat some random mid-tier P4, they would have been sitting home and Vandy/BYU/etc. would have gotten the spot. The ND win was their marquee win.
As for football in general - the Notre Dame fan base definitely trends old, but they all watch every game on TV and they have the money to travel. Three quarters of ACC teams are struggling to fill their stadiums, but the ticket vs. Notre Dame every 4th-5th (ish) year drives single and season tickets. The year we had Michigan on our schedule we sold out some pretty lousy games with a pretty mediocre team.
Eventually college football isn't going to be two-tier (P4 vs. G6), it's going to be three-tier (SEC+Big 10 vs. ACC-Big 12 vs. G-everyone else - all of this with some movement available). The ACC is definitely the first conference of the Power 4 that's going to be devalued down to the mid-tier. Notre Dame is the wild card for them. As for other conferences locking them out of their schedule, wait til you fill the Notre Dame home-and-home game with Central Michigan and see who shows up. This is especially true of a handful of programs that have fallen off a cliff the past few years (UCLA, for example) but also the ones who just recently started to struggle (Baylor, Wisconsin, etc.) - attendance isn't an issue there yet however that could change with a few more years of struggle.