In any and all cases, expansion is a two way street. While I personally believe the Pac-whatever-number-they-end-up-being would be beyond dumb to reject teams like OK and OKSt, in terms of the B1G it's not just about the conference wanting ND. ND has to want to be a part of the B1G, there are no hostile takeovers. With all the $$$ ND gets now with NBC and just in general from being independent, there are incredibly slim chances that they move to the B1G or any other conference in the near future.
Therefore, debating over B1G expansion that involve discussions about ND are essentially pointless, as much as I would love that idea.