Wow....very sorry to hear about your friend's unfortunate incident. It is too late for this but for others, as a rule of thumb, never track anything you can't afford to lose or write off. This is why buying track insurance is absolutely essential since getting insurance is something you control...what happens on track is something you can't control. 600 is far cheaper than a rebuild and salvage title.
Regardless, I would avoid calling your insurance and trying to have them foot the bill because you risk the chance of having the agent flag your account and drop your coverage altogether since you're pretty much admitting that you're using a covered car under policy for off road use (yes this has happened to others). I'd say your best bet is to sell it as on ebay or copart and try to recoop as much as possible. With the wait times and scarcity on parts, rebuilding might not even be a feasible option and might take months....if best case scenario, parts are available and the frame isn't damaged.
Even if you rebuild it with a clean title, your friend would need to disclose that it was rebuilt and accept a lower sale price if he ever decides to sell. Its not a situation I'd like to be in.....