resentment towards his parents for not having gone nuclear in a very similar situation.
Yes, the kid will probably be embarrassed that more people know about it by taking action. He may not like it in the moment. But in the long run, later in life, he will be grateful for parents that stood up for him. I believe it will make healing easier in the long run. This is sexual assault. The guys who did it should face huge consequences.
Move the kid out of the school if you have to; but definitely act on it.