Why would Notre Dame even think of being a part of the Big Ten?
What possible good does it do to join a conference right now? The school is mega-rich and doesn't need the money, it loves being the snooty Augusta National of the college football world as an independent that can do whatever it wants to, and the academics are strong enough that joining the Big Ten doesn't provide a big boost.
Remember that expansion has nothing to do with the sports on the field. This is all about business, this is all about TV markets, and this is all about money generated from ad and sponsorship deals, so the idea of Michigan vs. Notre Dame as a nice football matchup doesn't really mean anything other than the possible revenue created as part of a Big Ten TV package. But if Notre Dame thinks its brand name would be lessened by being part of a pack, it's not going to make the move.
Yes, Notre Dame would make more TV money as a member of the Big Ten than it would on its own with its current NBC deal, but remember, the school gets to keep all of its bowl money, it gets more than a million dollars a year from the BCS just by being Notre Dame, and football-wise, there's no reason the team needs to beat its head against the wall as a fourth-place team in the Big Ten when 10-2 means a BCS bid and 9-3 makes it a 50/50 shot as an independent. It's not like the school is going to lose a ton of money by not joining the Big Ten, and again, the place isn't hurting for the dough. Anyone who needs cash would've found a way to take the bowl invite it received last year and would've made it cost effective, and remember, for all the talk about Charlie Weis' contract and buyout, he paid for himself with the BCS appearances.
Don't forget that Notre Dame knows exactly who it is and where its place is in the sports and college football world. This is the one program that everyone wants, and if Jack Swarbrick and the powers-that-be ever decide that the time is right to join a league, it can do it at a moment's notice, while being welcomed with open arms.
Why do you think the Big Ten will expand to 14 teams instead of 16 if it doesn't get Notre Dame? The league wants to leave the door open in case there's an Irish change of heart down the road. Also, don't assume that the Big Ten is the only conference option. If the Domers want to go to the SEC, it's a done deal now. If they want to find a way to be a part of the Pac 10 for football, where do they sign?
Yeah, Notre Dame has other sports, and the non-revenue side of things - read, the other Irish sports teams - might like the geographic tie-ins and the short bus rides to Purdue, Indiana, Northwestern, and the rest of the Big Ten, but football is obviously king. The Big East's toothless threats aside, Notre Dame can do whatever it wants to and isn't going to care about any join-or-die declarations. When all the dust settles from Big Ten expansion, watch for the school to wait and see just how big the newly-formed league gets, take a few more years to weigh its options, and then decide what it wants to do around 2013.
There's no reason to do anything else.