The problem is that there isn't much DL can really do. It's not as though people who are prohibited from, encouraged not to, or are simply taking personal precautions, will purchase tickets because they are cheaper or DL throws an RDM their way.
Unlike 2007-09, carriers won;t simply cut prices to fill aircraft. Rather, they will reduce capacity to fill aircraft with people paying fares which sustain profitability (or less loss) and combine that with whatever bailout the government comes up with.
If it comes to the end of the year and there has been a significant hit, I am willing to bet that DL will do some kind of pro-rated status extension. That costs DL nothing and keeps the same customer base chugging when the COVID issues pass,.