On the charter boat side insurance policies are from all over. Voyage a few years ago used a company in South Africa. I suspect they still do the same. Moorings underwrites through Lloyds. There were some smaller companies using a local company. The average value of a charter boat payout I suspect will be closer to 200,000.00 if totaled, less if repaired.
I don't see how a company can just refuse to pay. They would cease to be a insurance company at that point. They could however fail which could be a nightmare for those of us who own boats. If a specific charter companies insurance fails I see know way the associated charter company would not fail so they have a vested interest.
One thing that will be interesting is how many owners choose to invest the insurance money in a new boat verses taking the money and running!