Two things.
One, there will be some amount of old fan attrition each season as it just becomes too much for whatever reason...health, finances, mobility. One answer to this is to actively encourage an "inheritance option" for Gopher points, seats, and perks under the right conditions. We had a fantastic but older seating neighbor prior to covid, who died too early during the lockdowns, whose kids used his seats (probably off the books) for a couple of seasons. We did not mind. For whatever reason they let them go.
Second, there has to be some small measure of season ticket growth...not just maintaining the current number but adding too it. Obviously the improved product on the field has not translated yet to in turn improve that number too. Mega's move was ill timed, poorly explained, and terribly executed but it's been 10 years. The in-game experience is great and better teams are being fielded. An expanded B1G also has improved the match-ups more often than not. Similar to the inheritance idea (if it does not currently exist), maybe a 7-8 year graduated pay scale for UM grads to get them to buy in or similar? Hard to believe this would lose money over the long term.