****, I hope its not too bad? Is he insured?
There are a few Spec S's on carzone etc for up to €10k, but they're not realistically worth that as you could get a decent spec R these days for €11/12k. If you were selling I would have expected €8.5-9k as yours is very clean but argue €12k with his insurance company and see how you get on....
Argue that the are very rare, well sought after and yours is a particularly good example with a high spec...
If it is not a write off make sure the work is done proffessionally and every part is replaced with brand new OEM Nissan parts or better (depending if mods were damaged). Do you have all of your mods declared?