I am quite sure that if UND left, UNO would quickly move to the MIAA - they are actually probably a better fit with the Missouri schools anyway.
I also am curious about USD. They have considered the move in the past - I am sure many of their alumni would really feel "left out" if the three other state schools from the Dakotas moved up. I truly don't know if they could afford it, however. I don't know if UND can either!!!