I swapped bikes with a mate on a ride last week ‘cos he wanted to ride my full-suss on one of the descents, he fell off and scratched the stantion of my brand new forks. Bit of a bugger but at the end of the day there’s as much chance of it happening to me as him.
What would your mate have done if he’d been the one crashed into at the race? If he’d have bought a new wheel then I’d say that’s what you owe him. If he’d have shrugged as he was given it free by a sponsor, perhaps an apology will suffice?