I have thought the same. Then you would need Clemson to well, Clemson. Bama to slip up against Auburn or Florida, or the Buckeyes to lose, but NOT to an undefeated Iowa team in the Big Ten Championship.
I think this weekend will be very telling. I think Ohio State will lose against Michigan State (assuming Cook is honestly good to go), and I do think the Boilermakers have a serious shot of knocking off the Hawkeyes. Last week the Pac 12 died, and I think the Big Ten has a chance to eat it this weekend.
Back to Oklahoma though, it would still somewhat surprise me if they won out and got in over a one loss ND team. This is based solely on the fact that ND's loss is on the road, in the rain, against the #1 team in the nation, whereas Oklahoma's is against the pitiful Texas Longhorns. Surely that would launch ND over OK even though ND won't play for a Conference Championship?