Let's think of worst case scenario. B1G takes Georgia Tech and UNC. SEC takes VT and NC State. Then they add Cincy and UConn.
Regarding Access: The Orange Bowl will still be considered an access bowl and the revenues will be on par with the SEC vs. Big 12 matchup.
Regarding Markets: The ACC will still have Miami, Charlotte, Raleigh, D.C., Pittsburgh, Boston, and strong ties to New York and Chicago with the Notre Dame, Syracuse, and UConn influence. The Big 12 has DFW, Houston, San Antonio, and . . . Tulsa? OKC? Kansas City? Topeka?
Regarding Prestige: Yes, Texas and Oklahoma are carry more prestige than FSU and Clemson. However, Pitt, Miami, Louisville, Cincinnatti and Boston College more than hold their own with Kansas State, TCU, Oklahoma State, Texas Tech and West Virginia. If Big 12 carries an edge, it is modest. That's also not including the affiliation with ND, which if included, the ACC would surpass the Big 12 in terms of prestige.
Regarding Revenue: The Big 12 currently has better tv revenue. But the ACC still has better media markets, similar bowl games, and a much better basketball brand (which isn't huge in terms of dollars but it does matter.)
When you take into account the poor leadership in the Big 12 and the concerns of alumni it is going to be a hard sell for the Big 12 to get any ACC to jump ship, even if they lose some teams to the B1G and SEC.