There would definitely be a large inquiry into the matter - if it could be proven as self-defense he would not be exiled but there would definitely be some other consequences (he could potentially, for example, end up fostered into a more disciplined guard family and given some very rigid training so he doesn't violate the rules and learns to act appropriately in a given situation). It's pretty open but he wouldn't get off scot-free. Due to his youth and the circumstances there would be more focus on rehabilitation in that case, although the methods might be a bit severe.