and did nothing about it, I think you might have implied consent, but if you immediately told him to return the car then I would say that he is accountable for all of the repairs. Another question, has he done it before without any repercussions? If so, that would also seem to indicate that you were okay with it until he hit the deer. If you want him to continue working for you then he covers the cost, but if not, you fire him for breaking company policy.