I submit there is a possibility, albeit not likely, ND can still make the playoff. Alabama, Georgia and Ohio State appear to be locks. If the Big 12 takes each other out, would you put ACC champion Clemson or PAC-12 champion USC in before ND, considering the Irish would have beaten these two one-loss Power 5 champions?
If this all plays out, I think the only way you keep ND out is if the Big 12 champion only has one loss. If they have two, they have no better argument than ND. Again, I realize all of this is extremely unlikely...but the possibility does exist.