The agreement is only verbal and there is no NLI since the school is not committing anything tangible to your son. If the coach leaves or get's fired then the commitment leaves with him. To the school your son is just another incoming student and will not be part of the team until school starts and the coach puts him on the list. Sometimes schools give priority registration and housing to student-athletes and he will likely not benefit in these programs, but I would check if your son decides to go there.