In just about any scenario, an undefeated ND team cleanly gets into the playoffs. We control our own destiny.
The only scenario I can see where we wouldn't get in, is if the refs give us a 5th down (like Colorado did in 1990) we win by a point because of the gift, and we stay unbeaten only because of that gift 5th down in both remaining games.
That's not going to happen. If the impossible scenario above did happen, and piss off the voters that much, then rest assured, they wouldn't give us a passive national championship.