Actually I don't think there's a section in the CBA regulating details on existing contracts if the season is canceled.
Therefore it's anybody's guess what would happen in that case.
While the new NFL CBA, unlike the NBA's, does not contain force majeur language with respect to player salaries, the standard player contract under the prior CBA contained this language:
"Player will be paid 100% of his yearly salary under this contract in equal weekly or biweekly installments over the course of the applicable regular season period, commencing with the first regular season game
played by Club in each season.”
The old CBA standard contract stated this provision would be in force for 2020.
The new CBA's standard contracts states:
"Player will be paid 100% of his yearly salary under this contract in equal weekly or biweekly installments over the course of a 34- or 36-week period during any of the applicable 2021 through 2029 League Years, commencing with the first regular season game
played by Club in each season."
It is implausible the NFL would not insist players share the pain in the event of lost revenue from games not played. Whether that old provision evidently applicable to 2020 is where the league hangs their hat or something else, I'm pretty confident the NFL will seek to cancel salary payments in 1/17 increments for each week where games are cancelled, perhaps not immediately but at some point. "Played" is a pretty concrete and specific word. That may be sufficient.
As for signing, roster and workout bonuses, any money already paid out is, well, paid. Those monies are earned by virtue of a triggering event. I would suspect that a signing bonus where the individual player contract calls for cash disbursements over some period of time that would extend into a shutdown period would be paid. I'm not sure if league year roster bonuses are required to be paid in full when earned or may be disbursed over time per the player's contract, but the same principle applies, money is earned at the triggering event, whether signing a contract or being on the roster on the specified date per the contract.
I would suspect that workout bonuses or per game roster bonuses, like salaries, could go unpaid if the workouts or games are cancelled since the triggering event did not occur. Like the NBA, the NFL may defer invoking their rights so as not to royally p*ss off their key employees.
This is all a little murky and a little premature. If only OTAs and mini-camps are cancelled, it would be fair to assume the season will start on time. Camps start in mid-July. I would expect if that extends into August, depending on when exactly, they would cancel some or all of preseason and start the season on time. There's just too much money on the line, for players and owners, to expect otherwise.
What's the minimum amount of camp to avoid opening day cancellation? I dunno but I'd guess it could be as little as two weeks. That, or maybe a little more, would make for even more sloppy football than what we see in the first 3 weeks of the season, as though very many across the viewing audience would notice or care.