Big difference between a shortened season and a cancelled season though. The way the NFL players get paid is extremely interesting, and with the exception of the "Elite few" veterans with the majority of their contracts paid via signing bonus's, a players base salary doesn't kick in until the first game of the league year. No first game, no paycheck.
Seeing how the majority of the NFL players would fall into the "not getting paid for 2020 category", and they are governed by a union, in which the majority has the power, hard to imagine there not being some semblance of a season.
Of course, there could very well be some Vets with contracts like Kirk Cousins (not singling him out here just a contract like the one he has), that could potentially sit out, but there is too much money at stake here for the players not to play. And I am not talking about the money from the owners perspective, but the players perspective as well.
The salary cap implications of a cancelled or shortened season, limited fans in the stadium, etc etc is going to bring abut some far reaching implications into next season, and the season after that. Salary cap could drop as much as 30 million next year, unless an agreement is made to parse that out over the next several seasons. As a result, you might still see teams THIS YEAR shedding vets to cut payroll, if word of a shortened season starts to become a reality.