I don't know anything about that. What is the purpose of that? It sounds like it's close to a salvage value (though probably higher if it's not an "at-auction" value), and that it is rarely used.Anyone ever used Immediate diminished value is the difference in resale value of a vehicle immediately before an accident and prior to repair?
Typically for diminished value you just wait until the car repairs are complete. Then make the claim after you get the car back. They are still on the hook for damage to the resale value of your vehicle. The claim is not closed. Make it promptly (since cars are always depreciating), but for now if they are proceeding focus on ensuring the repairs to the vehicle are done correctly.
I don't remember the details of your car other than it is a used vehicle. But probably at least several thousand dollars of diminished value. As I said, there are plenty of calculators out there. Hopefully you don't run into property damage limits.
There's no need to hire anyone to do the claim for you. If you do the research, you can simply send a letter to the insured's insurance company and ask for the appropriate amount. They will negotiate, etc., of course, but it should be able to be resolved, since it's fairly easy to evaluate the approximate loss of value, and it's not really something that is "wishy-washy."