Interesting story. Hard to condone cursing at a client, but from your description, someone needed to get their attention. Odd circumstance that you were laying out money for things on such a small boat. You must have been reimbursed or I'm sure it would have made the recap.
However, this premise has a flaw.
I told him we was risking my captains license and my retirement and I was not pleased.
Even if they had insurance, you are typically not covered. The insured party, the one who the insurance company protects, is the owner. 99% of the time, when the deliver skipper is "added" to the policy, it is only as an authorized operator. That means the owner is still defended, if the authorized operator causes a loss, but the operator is not defended, unless they are added as an additional insured party. Most call their insurance company, explain the delivery and get a rider for that captain and those few days. The insurance company is often only saying, "sure, I will still cover your losses when that bloke is driving your boat on those days". What they are thinking is, "I'm not covering that blokes liability and if I have to pay the owner to repair the insured hull, I will just subrogate my loss and sue the captain, since it was their fault". That's why people are often surprised that the rider is fairly inexpensive.
In the industry of skippers and instructors, I am very surprised how many consciously go without coverage. Many actually accept it, others just aren't aware.
You want to be an additional insured party or have a waiver of subrogation on the clients policy and your own liability coverage.