Now let me get this straight. They had PAID IN FULL for the cruise. They were making their own travel arrangements. It was 4.5 hours before the scheduled departure. And Regent "had no idea they were going to show up that evening" so the Captain pulls away. What an absolute unmitigated piece of crock. What if they had booked a quick independent tour of the island before boarding the ship? Or they were meeting friends for cocktails before boarding. Or they wanted to do some shopping before boarding. And even if they had submitted flight details to Regent (something we have never done or, to my recollection, been asked to do), does this mean Regent thinks they have no right to independently change those plans.
I think a $500 credit is an insult. That is about one half the cost of the night they lost due to Regent's negligence.
Patrick