My theory is that Miami was pissed off at the image of the big east, coming off a national championship and having the media paint a picture of the conference as weak, basketball oriented, everything we know about. Miami wasn't in a football conference with notre dame, and stopped playing them for a while after 1989, b/c they were both independant until 1990, when the big bowls got together and formated the coalition, or alliance or whatever and tied themselves to conference champions.
Miami wanted a stable, and well respected football conference. They wanted Notre Dame iether in or out, not half way. Getting Notre Dame in - ideal. Getting Notre Dame out- solidarity.
The ACC offered a lot that makes sense to Miami, as you noted. What they didn't offer was Notre Dame. What Notre Dame IN would have done, is immediately validated the Big EAst conference as a football power, which would have taken the media tarnish that the 2001 national championship had. Notre Dame being ejected from teh big east, OUT - would not have done the same thing, media wise to validate Miami's presence as national champion, but it would have been the most clear sign, and it still would be the most clear sign, that the conference was no longer being ruled by basketball interests, and therefore would have been stronger in the future.
Would ejecting Notre dame have prevented Miami from eventually leaving? WHo knows. You didn't ask for a theory as to how Miami could have been prevented from leaving.
But had Notre Dame been given the call in 2002? I believe if they were ejected in 2002, the conference would have been stronger going forward, because to eject Notre Dame, would take leadership that valued football above anything else.