For a subfleet of 10, and many of the planes parked previously destined for 2022, it should not be impossible to fathom that a handful could be reactivated to allow for proper economies of scale. If the economic trend nosed up a little, as the curve shifts. Particularly if many of the aircraft remain stored and not scrapped. (They won’t need to cannibalize all the recent parkings immediately). Given the situation is clearly fluid. I wouldn’t bet on it per se, but it shouldn’t be ruled out as an absolute 0% chance, just yet either.
If reactivated soon, I can see that scenario. However, if time progresses and substantial re-activation costs must be incurred, it will cost to much to restart the fleet.
Looking at old quotes, it was over 20 aircraft to be retired by 2022, or in other words to 2021, There were a number, with my interpretation of this link that 9 weren't long for the fleet of the 32 (I assume due to the need for expensive maintenance checks):https://simpleflying.com/delta-md-90-retirement/
The cost to reactivate is trivial in two weeks. In six months, it will be too high to justify flying in only 2021. So between now and October we'll find out.
The question is, how much demand will recover by October. I hope to be wrong, but I doubt there will be demand by then.
Flu+Covid19 is bad. Consider a flu vaccine, if not for yourself, to protect someone you care about.