Common sense would say that the shop screwed up but we both know that they're more than likely going to fight it to the death. At that point it's going to be necessary for the OP to prove that the shops negligence caused the fire. If that's even possible.
I'm not suggesting to just go straight to his insurance company, definitely try to get the shop to pay for it.
original posts says the shop's ins co is going to cover it...
i would personally involve my own ins company to act as my agent in the deal. i've done it before and if you have a good agent they will not hesitate to help you.
a big on-line company like Geiko or progresive, maybe not so much.
they arent going to buy you a new vehicle, they simply arent going to do that, and if they did, it would be suspect immediately.
get actual price quotes from several dealer websites and even rip some pages out of the "wheeler dealer" advertiser magazines in your area.
produce nothing less than 5 legit ads in your region for a comparable vehicle and push them for a payout on the highest one, and maybe compromise on an average of the 3 or 4 most expensive ones.
take the check, say goodbye to the burned-up rig (you will never reach the end of the electrical gremlins that will be running around in the rig after a fire) , and start shopping with cash in your pocket.
good luck, let us know how it works out.