I think the charter company accommodating people for situations like this goes a long way. I have done this with my beach house various times for guests with issues or situation changes...

I use Moorings for this very reason and I know there are other charter companies out there that do well by doing it right. In this case they said give them as much advance notice as possible but it has to be greater than 15 days for a credit to rebook by the Fall.

Unless there is more to the story (e.g. your charter is a couple of days out) this really surprises me