To my understanding, any ticket booked with Delta prior to May 31 is able to be changed or cancelled without a fee or penalty but the credit will be in the form of an e-credit, good for 2 years from the booking date. There is also some language pertaining to travel prior to Sept. 30 and the supervisor I spoke to said things would be updated at some point for travel after Sept. 30. This is all new for the airlines as well. The quarantine thing would be a deal breaker for most people unless they are very long term visitors.
As per Delta policy, if THEY cancel the flight or change the flight time or connection by MORE than 90 minutes, it is a refund (if so desired) back to the original form of payment.
DELTA CHANGE POLICY