Tough deal for sure but as already noted, this makes absolutely no sense. Coaching at the collegiate level is a business and those who don't treat it as such, don't survive long. I have an incredibly hard time believing that a HC would cut this type of player for no apparent reason. I am familiar with numerous situations where an elite player is sent packing but in every case it was due to a violation of NCAA, school, or team rules. Also aware of a couple of "cancer in the locker-room" cuts but sounds like your son was liked by his teammates.
I am assuming that someone on the staff sat him down and shared that he was no longer part of the team? If so, there was no reason provided as to why?