Padilla's longest drives did come fairly early in each game. He had trouble finishing them, coming up short either in the red zone or just before getting to the red zone. They did use his mobility effectively, either rolling him out or moving him around in the pocket. He was rarely sacked.
Petras has a lot more experience and a better arm, if he has any time to use it. No doubt, Michigan is going to bring it against Petras, the way they did against Stanley in 2019. While Petras isn't likely to totally freeze the way Stanley did, he may not have time to throw the ball with any effectiveness.
If Padilla came in, it would be because the offensive line and Petras are not effective. A lot of Padilla's plays already try to compensate for poor pass blocking. So, it wouldn't entail asking Padilla to do something much different than he has already been trying to do. Playing Padilla if pass blocking is a major issue, might be feasible.
So do you put Petras back in when you get within striking range of the goal line. They might want to consider that. They wouldn't want to put Petras in for long yardage plays, where he's likely to get sacked. Better to put him back in on a first down.