Even excessive damage which would surely be considered a write-off can be repaired satisfactory within reasonable cost.
For example, this 2010 Mercedes C250 AMG was involved with a serious accident and the insurance company wrote it off. The customer decided to buy back the vehicle and repair it.
The car was jig worked in order to return it to factory measurements on the A & B pillars, a new roof skin was installed, a new front windscreen, a new bonnet and grill and a repair on the front bumper, doors and wing was performed. The car was sprayed with perfect colour match and resulted in a perfect finish. You wouldn't be able to tell this car was ever damaged, let alone having a serious damage as above.
The final outcome: