If the car was taken to a Good Factory Authorized (ASE, I-car certified) Body Shop, the repair should be made to factory specifications and done correctly. Second any good body shop will offer a life time warranty on any repairs they performed. Most body shops around here do. If the car was done this way and not in a chop show with 1/2 a car welded to it, it will be fine. These body shops have to answer to their insurance companies for liability and they are not going to repair a car they feel cannot be repaired properly and return the the same safety standard the car had when it was new. As far as diminished value, I think you’re heading the right direction having it evaluated and finding out if it was reported to car fax is good idea. Have pictures fo the damaged to show them. If it has been hit hard regardless of how it was repaired it will affect the value. That is just a fact of life. If you spend $20K fighting the insurance company you might for $10K back. Next time look at purchasing new car replacement insurance on your car it’s usually not very expensive.
I'd seen commercials advertising new car replacement options on insurance, and never thought it would be worthwhile. I'm definitely a believer now.