mark my words, the NFL will be playing a full schedule. No pre-season games, but all of their regular season games. Why? Because the economics are different for the NFL than they are for the NBA and MLB.
Here's some simple math. Each NFL team made $275 million last year just in NFL revenue share from TV deals and merchandise licensing. This year's player salary cap is $198 million and many teams are below the cap. So even teams with no fans allowed will be strongly motivated to play because their losses from general overhead and other fixed expenses will be far worse for each game that is not played.
MLB and NBA teams, OTOH, rely much more heavily upon gate receipts and concessions for their revenue. MLB teams are actually losing money for each game played without fans this year and, if not for the fear of a long-term fan revolt, the owners would have gladly foregone the season altogether.
As far as NFL players sitting out, please already. The vast bulk of players of low contract guys who can't afford it. For the remaining 20%, most of them aren't going to give up a whole season payday. There may be a few high profile veterans who have already made a shit ton and can afford to do it, but not enough to seriously impact the season IMO.
I can't wait for NFL football to start.