Once insurance had made the decision, it doesn’t matter about NHTSA, they are not going to wait forever; not sure what NHTSA needs, Tesla should have all the data and you have all the photos and possibly the police report ?
I am not in insurance business or lawyer, but to me it seems you have limited choice.
1. Accept the check and move on.
2. Negotiate with insurance about the payout, but you have to prove the market value of the car is higher. From used car perspective, most fancy options are worthless and doesn’t add much to market value. FUSC is not transferable, so insurance may say it’s $0, FSD may not worth much either, used market may not look at it as desirable with high dollar amount, and people can always subscribe instead of paying large amount of cash, but only your insurance company can answer.
3. Keep the salvage title and the car, taking a big cut in the settlement. There may be state laws governing the legality of this.
4. Find someone who will fix the car for a lot less than what the insurance determined, doubted you will get anywhere with this.