My mistake on missing it is a day school. Still, it is against school rules, clearly laid out, and second offense. The student in question took a known risk. At 18, one can’t claim it is overreach when he is old enough to be responsible for his actions. It’s not the end of the world. Many colleges would be happy to still have him. It just may or may not be the one that accepted him early. A lot will depend on how the student chooses to address the infraction with the current school and the college in question. Again, the expertise of a consultant would likely be worth the costs.