I think if we lose a game, any game, we'll fall behind Michigan in the rankings. Then, assuming they beat OSU and run the table, there will be a loud argument from many quarters that a 12-1 conference champion who beat OSU, Penn State and Wisconsin (twice?) has improved significantly since the first game of the year and is more deserving than a one-loss ND team that only has one marquee win (never mind that it's over that very same team).
These people will not care that we, too, have improved significantly since Week One, or that the Michigan game wasn't even as close as the final score. And they may not win the argument that head-to-head results don't really matter.
But I'd expect there to be a lot of noise to the effect that Michigan should get in over us, based on "momentum" or "the eye test" or "who's playing better right now." Especially because we really don't have any games in the second half of the season that will impress anyone (despite playing USC, FSU, etc.) It'll be infuriating, and it might even be successful.
Best way for us to make the playoffs is to win 'em all. If we lose one we have to blow out the rest of them, because there is a strong bias out there in favor of conference champions. It would also really help us if Stanford could somehow turn it on and win the Pac 12.
Or, as is also quite likely of course, Michigan loses. We'd get in over OSU unless we have a loss as bad as theirs to Purdue.