OP, I know you are probably sick of hearing everyone here telling you your son needs to man up and talk to the HS Coach and try to fix things with him, but its true. I know HS baseball is a minor point in the recruitment process but many college coaches will call the HS coach to verify the kids character.
I ran track in college (i know its not baseball but..) and I can tell you once you are in college the coaches take absolutely no BS. If they fell like the athletes character is not up to par they will deal with it. Some may talk to the athlete first others may react as your HS coach has and just eliminate them from the team. It does not matter if its an attitude on the field or an off the field incident. When you show up to your team organization meeting before the season starts the team rules will be explained to the athletes. Most schools will require the athlete to sign an agreement recognizing the rules. If you break one of these rules it will be dealt with. How its dealt with is up to the coach. He may go soft on one kid and boot another. Its totally up to him and the athlete has no say. It may not be fair but thats the way it is. Its better for your son to learn to deal with these issues now instead of trying to navigate through it later in his career.