Well, that is the "elephant in the room" question, isn't it. The big "what if" question.

There is a hospital, CH Louis Constant Fleming, in Marigot. IMHO, it's a decent local hospital, but it's not the Mayo Clinic.

You also need to think about the cost of treatment, the potential cost of Medevac to a larger French island, or the potential cost of Medevac back to the US. Or not. It's your choice how much and what type of risk that you take on. For what it's worth, the last Medevac of a patient to Miami that I am aware of was months ago, but I may have missed one.