I think the REAL test is when the season tickets go on sale.
Ditto. Viewer ratings for TV may be a good precursor signal for the NFL, though as the OP notes a lot of non-fans tune in just for the “big game” just because its a spectacle. Ticket holders will (mostly) go because they’ve already paid. It’s the ticket sales for next year’s season that will be the big referendum on the NFL. There were a lot of empty stadium seats this year, even for games that “mattered”. The real question is, how many people who actually showed up for those games only went because they’d already paid, and didn’t want to completely waste the money? Are those people still going to show up next year?