Worst case, schools would have 5 years to get back to normal, as they can redshirt some 2020-2021 incoming freshmen. A more reasonable case might be 3 years. With kids leaving the program via transfer, grad-transfer, pro-contracts, injury, homesickness,... things should work themselves out.
Just my assumption, but any 23+ year old young man who feels that their "pro clock" is ticking isn't going to want to spend an extra year in college. There are always a few guys who don't see themselves having a pro career that might stay around for that extra year. The ones that stay at their original university will be a low number, maybe one or two per class. There could be a significant uptick in the number of grad transfers as school is/was still in session. They will be graduated with an extra year in hand. This could ease a lot of the burden on the roster and could really help St Thomas and Long Island be competitive and be more selective about recruits they bring in.