Back in the 70s, I worked for a custom body shop. The owner, Al Watson, always told me that any car can be fixed, no matter how bad the damage. It all came down to what you wanted. If it's some family sedan that it's going to cost you hundreds of hours and thousands of dollars to fix, it may not be worth it to you. It can be fixed, but do you want to? If it's a 1968 Ferrari Daytona Convertable that's worth a half mill, then the time and money is probably worth the costs. All comes down to what you want.
When I re-kit a plane, it sort of depends on a couple of factors on whether it goes into salvage mode or is repaired. How badly it's damaged "usually" doesn't enter into it (I mean, if it's scrap; bit of parts and no two pieces still glued together, then the exercise is academic). What I look at is: Was it a good flying plane before the crash? How much weight is likely to be added with a repair? Can this design stand the weight gain? And most important, will it be easier to repair the plane or build a new one?
Sometimes it's isn't all that easy to decide. I have a Novi sitting in my plane rack awaiting a decision. It needs an all new outboard wing. Probably need to be stripped back to the wood, rebuilt and refinished. It was a great flying plane and the repair will probably result in a lighter plane since I will have to refinish and the original finish was no lightweight. The question remains, is it worth it? I haven't decided yet.