State law where the accident occured makes all the difference, for instance, in Washington, they can't total a third party's (that would be your son) vehicle without consent. A woman pulled out in front of me hauling a horse trailer while I was doing the speed limit, and told the Cop that not only was it her fault, but that she "should have been wearing her glasses". I got $6500 to repair a 76 Goldwing that cost me $1000 (plus a lot of work and parts), and fixed it for free with spare parts from donor bikes I already had. It only "blue-booked" at about $850, but I had restored it a few months ahead, won a "best foreign dresser" award recently, and was on the last leg of a 5000 mile trip. The $6500 figure was a Honda Dealer's estimate to repair the bike to it's excellent former condition, and they complimented me on the work I had done. It is in the garage waiting for the snow to melt. In California, they pay the lesser of replacement value or repair. I bought my wife an 85 BMW with new paint and a bad auto trans, and rebuilt the tranmission, suspension, engine, brakes, etc and made it a fine car. It got T-boned in California by a woman who admitted fault, and her insurance, Farmers, looked in Autotrader and offered $3800. My state licensed independant appraiser evaluated the car at $9100. Farmer's wont negotiate, so I am suing the driver of the vehicle in small claims in a couple of weeks for the maximum of $7500. I have much documentation and am confident of a win. I'll bet she isn't happy with her insurance company now!
Bottom line, Check the laws for Montana, Talk to an insurance agent who is IN Montana, not of a company involved in your son's accident , and check to see if Montana state code is available online. I would bet that Montanans have better protection from insurance companies than Californians.