One thing I haven't seen discussed here, and I think is the lynchpin in all of this is the players union. I cannot believe for 1 second that the union would allow game checks (that are contractually agreed upon) to be forfeited because of something NOT contractually agreed upon. I don't believe (i've never actually read it but i've never heard mention of it) anywhere in the CBA does it say anything about check forfeiture. As stated earlier it's going to be borderline IMPOSSIBLE to be able to isolate the 'cause' of an outbreak, so if the NFL threatens to cancel a game where 5 members of a team who are unvaccinated catch Covid, the first thing the Union is going to say is "prove to me this didn't come from an asymptomatic carrier that WAS vaccinated."
The start of all of this was the differences in training camp and team activity allowances depending on how many of your players have been vaccinated. The more players that have gotten the vaccine, the more involved and inclusive your practices can be. It doesn't take a brain surgeon to figure out that less time together than the team you're playing against is a disadvantage. It's going to result in vaccinated players on the bubble having an edge over an unvaccinated player when rosters get cut down, so teams can attempt to get over that threshold of less restrictions.
The NFL has been trying to push more and more players to get vaccinated for a while now, and while technically it's a job and it's not a right, the players have a union to protect them. The NFLPA and Union will likely be pushing the players to get the vaccine to limit the amount of times they have to get involved, but if a game is cancelled because of an 'outbreak,' the Union is going to be all over it on behalf of the 50 - 100 players that were not positive.
The OTHER factor in this is money. If a game gets cancelled, that money is lost. Ticket sales, concessions, merch, parking, player income tax from BOTH teams. TV revenue. What happens if this effects a MNF game. That's the only game that week for ABC / ESPN. No chance they just let it happen. What if it's NBC giving up Chiefs vs Bills in week 5 on SNF? I just can't see the NFL actually pulling the trigger on it.
The games will get played imho, and the NFL is laying the groundwork to justify it. They're leaving doors open to get it in, but make it look like they're coming down hard. They've done it with ALL polarizing topics surrounding the game. BLM, concussions, domestic violence... The tone is always the same.... hard stance to show they 'care' but plenty of wiggle room to make sure they don't lose any money.