"subrogation" is a term pilots through around to keep each other up at
night. In truth is an extreamly rare situation that is very expensive
for the insurance company. Insurance must be evaluated just as you do
any other financial decision. Its bunk to say you should buy as much
insurance as you can afford. In truth you can never assign all your
liability in life to insurance companies. Therefor, you have to decide
how much you are willing to pay to reduce your liability exposure. If
the guy has little assets there is no reason for him to buy a bunch of
insurance. You have to assume the owner has insurance that covers
himself (and the plane) when renters are flying the airplane because
renters insurance does not provide that coverage.

-Robert