If you pay for NCB protection you wouldn't lose any. But to get around this many insurers just add a bit to the premium if you have a fault claim so it can be a bit of a "no win" scenario. There shouldn't be any excess to pay for damage to his car, excesses usually only apply to damage to your own car.
In your situation I'd try to persuade him to get an estimate from a bodyshop (or two?) of his choice then give you the option of paying yourself or putting it through your insurance.
In your situation I'd try to persuade him to get an estimate from a bodyshop (or two?) of his choice then give you the option of paying yourself or putting it through your insurance.
