Each school will need to decide how to accommodate this and keep students relatively safe.
As for ND, the Navy game will be canceled or hopefully moved to Oct 24 at Annapolis assuming Navy can change their game date with Houston. Opener will be Sept 12 vs Arkansas. Practices will be later than normal For ND since the season start will be set back 2 weeks. There may be fewer days of practice too.
I would be surprised if seating capacities were not reduced by at least half. 35,000 for ND home games would not be surprising. There will be no games played without fans. Reduced revenues but still plenty of TV money.