There is no good answer to your question right now.
As of the time when scheduled service was suspended, passengers who had been in the US (and a list of other countries) within the previous 21 days were not permitted to enter Sint Maarten.
At present, the only flights operating into SXM are recovery flights. No inbound passengers are permitted, including residents. There is a Delta aircraft on the ground right now.
Sunday, March 22 was the last day for residents to arrive. No flights, even for residents, will be available for at least 2 weeks from that date.
https://www.sxmairport.com/includes/images/press/2020/Prime-Minister-Jacobs-Travel-Restrictions.jpg
It's too soon to tell what will happen with the April 9 flight. The airport may reopen to scheduled service, or it may not. There may or may not be restrictions on passengers from the US.
As a general rule of thumb, which may not apply today, if you choose to cancel or change your flight then the best you can hope for is a credit, but if the airline cancels your flight then you can get a refund. That is what AA appears to be doing. JetBlue appears to be only giving credits. I don't know what DL is doing today, or what they might do closer to the travel date. The best that I can suggest is to scour DL's website to see what changes they have made to their Change policy, and read their Contract of Carriage.