Although 2018 numbers, the following article provides insight on how much is made from TV revenue/BIG 10 sharing ($47.9 mil), ticket sales ($37.2 mil) and endorsements ($25.8 mil). While TV revenue is big, ticket sales is not that far behind and a reason why Nebraska always operates in the black.
As it relates to the original question, safety is the key and in my opinion, a good portion of the season ticket holders are those most at risk of COVID-19 (over 60) I don't see how you could guarantee safety even with a good portion of the stadium empty. Another consideration is "break even" attendance to even out the cost of putting the game on. Not sure what that is, but if we assume its 1/3 of the stadium is it worth the risk?
Nebraska posted a $6.6 million operating profit in it's 2018 fiscal year that ended in July according to NCAA records.
nebraska.rivals.com