Is there any evidence the lack of medical was the cause of the crash? The NTSB didn't think so.
Is your contention he should be denied insurance despite the fact that the rule he broke was completely unrelated to the cause of the crash? If so, why stop there? What if he was fleeing from robbing a store but was otherwise legal? Should he be denied coverage because of that? After all, the crime is unrelated to the crash but he did just break the law, not just an FAA regulation. Or, is it just 'anything' you decide is related to aviation? So, if you knowingly fly one day out of 90 currency and crash should you be denied coverage? How about if you knowingly fly 1 pound over gross and crash due to running out of gas? Heck, there is a reg about carrying sufficient fuel so why isn't that a deliberate violation... I mean, you must have been cognizant fuel was low but deliberately and knowingly continued on anyway. Deny that coverage, right? Flying to your annual a few days after your old annual expired because of a weather delay?
This guy, even per the NTSB, didn't crash because of lack of a valid medical but from spatial disorientation. Why do you feel he should be denied coverage for something unrelated to the crash? A better argument would be that he was out of instrument currency. So, we are back to who is the arbiter of how far out is too far out before coverage is denied? I'm comfortable with the insurance companies making that call.
I guess I'm just tired of all the holier than thou Monday morning QBs looking for any reason to deny insurance coverage so their precious premiums don't go up. The worst are the ones that want to deny coverage for gear ups! But the moral high ground argument (oh, he broke the 'rule' so DENY, DENY, DENY!! I'm so righteous.) are tiresome, as well. Ever knowingly drive over the speed limit? Think your auto insurance should be denied if you crash while speeding?
How about someone injured by your illegal actions, be they in an auto or an airplane? Should they be denied compensation from your insurance because you broke a rule or law? How about your example: you let someone drive that isn't licensed and they injure someone in a crash and you don't have assets to cover since the insurance denies coverage? Does that seem just? Change it up a bit: your unlicensed hypothetical driver is in an accident that is NOT his fault; he's sitting at a signal and is rear ended at a stoplight by an uninsured driver. You okay with your insurance denying coverage? How about if someone else in your car is injured? Still okay with coverage denied?
Be careful on that high horse; the fall may hurt more than you might think.