Nick,
I am glad that you have now made the effort to contact Jimmy Buffett through the proper channels. It will be interesting to hear what, if anything that they have to say about the event in question as it is now months in the past.
I am a bit disappointed that you did not let the management have the opportunity to handle the situation when it occurred. Businesses are run by people. And people are not perfect beings. When you own a business, you strive to do your best, but sometimes not everything is perfect. That is why there is a manager on duty to handle such occasions.
At Margaritaville, I have witnessed first hand how the management deals with problems, and in no case did the manager suggest a free drink as a solution to the problem. But they did do everything possible to make sure that the food was prepared to the patron's satisfaction. In the one case I witnessed that they were unable to do so, they comp'd the entire bill for the party at the table.
You may feel that "a one and done" mindset is the problem, but that is simply an assumption on your part. Had you taken a moment to find out whether this prejudged feeling was accurate by contacting the manager, maybe your original "angry letter" would have never been made in the first place.