The NFL generates $11 billion of revenue annually. $3 billion of that comes from butts in the stands. That includes parking, concessions, game day merchandise, etc. The remaining $8 billion come from contracted revenues with broadcasting partners. The total revenue will absolutely be down. But $8 billion still places the product as a huge success. Sure, angry fans may not buy merchandise. But the vast majority of fans worldwide are not angry. As for viewership. Every person that would have normally been in the stands will now be tuning in instead. Viewership in one small demographic may indeed be down. But that will not offset the rest of the population that is starved for the distraction of the actual game itself.

And don't worry about the future earnings and contract implications. COVID-19 will have hundreds of times more effect on those than the supposed refusal of a small minority of fans that actually do decide to "tune out". Those concerns are already being addressed by the league and the NFLPA as we speak.