Caught in limbo with insurance & body shop on old car

Howdy. I'm in a bit of a quandary. I have an older car (1989 Mercedes 420 SEL - weekend toy, not a daily driver) that was involved in an accident way back in late May. The other driver t-boned me and tore up the right side of the car including both doors. He was found completely at fault. Much to my amazement, his insurance didn't total my car. They gave me a down payment to get it fixed based on the initial assessment from my pictures.

Most body shops didn't want to work on it because of its age, but I finally found one willing to do the job and they are associated with the other driver's insurance company. They've been able to locate sources for all of the parts, but there is a problem. The manufacturer that makes the front door has it on backorder with absolutely no ETA. The body shop placed an order (they haven't ask for any money from me yet) and they say they're confident this company will make another manufacturing run and deliver the part, but they obviously can't say when. I am not so sure. I have asked and they say they can't find any other sources for the part, including any used doors in good enough shape. So I've been in limbo for months. I have a beat up car that is unsecured (the right rear window won't go up due to damage in the door), no idea when (or if) it will be repaired, and the insurance company doesn't want to total it out because their replacement estimate (\~$11k) was way higher than the initial repair estimate ($6,300).

I dig this car and I've put a lot of work into it, but at this point I really wish it could just get totaled. Do I have any way to force the insurance company to total it? If not, and if I can't get any firm date from the body shop, can I just keep the initial payment from insurance company, cancel the job with the body shop and sell the car for parts? I would obviously rather have the much higher payout if it's totaled, but the $6,300 was more than I paid for the car, even after adding in all the new parts I've installed. Any insight would be appreciated.

EDIT: Thanks for the responses. To clarify, the car is still drivable and it's been in my possession the entire time, not at the shop.