The receivers never disengaged from their DBs nor did they ever give the impression that that was their intention. If they'd tried to sell it at all, they may have gotten away with it. True that FSU blew the coverage. But ND's receivers committed a penalty on that play, too, and that supersedes the blown coverage.
I would agree with you that they never disengaged, however, that doesn't and shouldn't supersede blown coverage.
Fuller didn't do anything illegal either. His block came right when the ball was thrown and it was after his defender idiotically jumped inside. In fact, his defense also engaged him.
FSU got bailed out for bad defending. Maybe you call that earlier in the game (I'm aware of the first touchdown 'pick' play). But not on the last play. #20 had nothing to do with the play and it was just two guys locked up at the line of scrimmage. Maybe he was blocking, maybe he wasn't.
Let the play go. The only way I throw a flag on that is if the receiver impedes a defenders path to the ball, which didn't happen. Fuller's defender blew his assignment, which resulted in the touchdown.
Fuller's defender also initiated the contact.
OK, so I just saw the first ND today. That IMO is offensive PI, morso than the last play. Receiver was not chucked at the line, sought out the defender and engaged. Impeding the defenders path to the ball.
Completely different than the last play. FSU defenders initiated contact on both receivers and #3 messed up going inside.
Maybe it was a make up call from earlier or maybe Jimbo complaining about the first TD influenced the call. Whatever the case. That is not offensive PI, especially on the last play of the game.