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It looks like you misunderstood the question.
It's not whether it's worthwhile to repair, but about how much money he can get out of the insurance.@Kaaaaaaandries
pick up the phone and call around a bit to decent frame builders and good guy bikeshops and ask them how they approach insurance valuation. It can vary wildly. My favourite shop over here base the value on what a similar bike with the same components would cost new in his shop, which can be quite a lot for rare, old or custom stuff.
Valuing=/=repairing