I too have had a son at a school where bullying was swept up and discarded for the sake of the school's reputation. The welfare of the kids takes second place but schools were ESTABLISHED in order to keep kids safe and show them some good moral guidelines, in addition to education. The school is failing in their duty of care to both kids.
It shouldn't become about the welfare of the bully, but it often does. Not wanting to be insensitive to the forces that create a bully, our society as often as not goes too far the other way.
I have some suggestions, don't know how practical. (I'm going to word it forcefully, obviously none of this is compulsory
There has to be a meeting where S has an opportunity to confront, we'll call him B, for bully, with those x-rays. If there could be a qualified person there to make some assessment of whether B's remorse was genuine, so much to the good. All cost to be borne by his family.
If S decides not to press formal charges there are still plenty of ways that B can contribute to his community to show his remorse. Do hospitals still accept volunteer labour? Community visitors? I don't know, but this boy needs some empathy training and supportive contact with people on a trauma or ortho ward would likely give it.
If it is possible to defer his entry to the Marines by six months while he fulfils this obligation that is the price he pays for failure to control a vicious impulse. If it could be enshrined in a legal document, that would be good, too. The financial costs of this might make the parents think, some people don't understand unless there is a penalty.
His, and his parents, willingness to try to atone will be a very good measure of genuine remorse. So often it becomes a case of "But I SAID I was sorry. Waddya want from me?"
For me, it comes down to whether he is genuinely devastated by his unconsidered action or is now just looking, with his parents, for a way to avoid consequences. The fact that he HAD that impulse at all doesn't say good things about him.
I'm sorry, I've made it all about the bully, too. But I am trying to find a way that S can be assured that this kid understands what he did without having to bear the (unfair) guilt of making him bear long term consequences.
I wish it was possible to have a uniformed police officer in that meeting but I'm pretty sure once they know about it they have to proceed. ?
My son did something silly, in the way of destruction of property, with a few of his mates once. Our local cop gave him a very stern lecture and made them repair the damage, but avoided formal proceedings. I've always admired the approach, but this requires something a little more concrete.
I really feel for S. Somebody has hurt him, unfairly and intentionally, and the attitude of the school has made it necessary for you and him to accept the responsibility for seeking a just outcome. That was their job.
Sorry about the extended rant. Love.