If the Sooners win out, and that's a HUGE if, then the Sooners are in, period. It's not possible for the Big Ten to get two teams in because of remaining matchups, and the SEC is a mess that probably gets messier. Same for the Pac-12. Clemson's unbeaten, but when you look at their schedule, it's pretty weak. A 1-loss Clemson wouldn't rank above OU, period.
Notre Dame has one loss, but a very rough remaining schedule that I don't think can be conquered. Notre Dame is good, just not that good. Thus far their schedule has been soft, and they haven't been all that impressive in their wins. They would probably rank right with OU if both teams won out, but I think on second look that OU will win out on schedule strength.
It' my opinion that if the Sooners surprise by winning out, there's almost zero chance that they wouldn't be included in the top 4.