I had a similar issue with my Ex Wifes car.
2009 Nissan Cube, it was exactly 1 year and 2 days from purchase, 10k miles on it. She was at a stop sign and was rear ended. Car though, was only $15,400 loaded (I'm a good negotiator), $6k worth of damage. They wouldn't pay Diminished value. They stated "We don't legally need to pay that". I said, I don't care. They refused. I then faxed over a copy of a law suit where a individual in WI sued a insurance company to get diminished value, send along a posted note on that document when I faxed it telling them I get diminished value or we will be re-producing this case in court. They agreed to Diminished value. So I took it to Nissan to get appraised, they wouldn't accept the appraisal as Nissan Dealer is "biased". Took it next door to a Ford Dealer, they wouldn't accept that one either, as they are biased as I could go and purchase a new car from them.... Finally found a Independent appraiser about 30 miles north, took it their, now, mind you, both appraisals I got from the dealerships were around $1800-$2200 in diminished value.
Now, the Independent appraiser, had past dealing with said insurance company (as in, they screwed him over tehe). So he gave it a $4k and some change diminished value appraisal. Now, I record all phone calls with insurance companies, as I deal with them for work (body shop). Faxed that appraisal over to the insurance company. They didn't want to pay it. Instead, they wanted to THEN go with the lower appraisals from the two dealerships. I said no, and that I had it recorded that they would not accept the appraisal from a dealership, and only a independent appraiser. So, to make a long story even longer, got the $4k

They definitely were NOT happy. Now, the medical, still working on that one 3 years later....
So, I got $4k diminished value on a $15,400 car. Before the car is even finished being reprieved if it is not already so, have a Inde appraiser come in and appraise the car for diminished value. I would also do a google search for a court case showing payment of diminished value of a auto that was won in court. It is still possible to get it totaled, and get reimbursed for extra costs incurred (gasoline) for having to drive a ICE, then valah, you get new car.
Questions, send me a PM and I will give you my phone number.