Think about it, there's really only two options if they don't play a season:
1. Every team is put in a lottery and one team gets lucky and picks Trevor Lawrence and another team gets screwed and picks 32nd, when no games were played. It'd be ridiculous.
2. The NFL coordinates with the NCAAF and states there simply will not be a 2021 Draft, with the NCAAF letting everyone have another year of eligibility. This would completely ***** over anyone who stayed for their 2020 senior year rather than declare for the NFL because they'd lose out on two years of NFL money AND then the 2022 Draft would have twice the number of eligible players and you're ******** over tons of players since only one draft covers two years' of players.
Or, you do the sensible thing and fit in some sort of NFL season and allow for the team records to dictate the draft order, as is customary.