It can feel like such a slap in the face when the goal has been a particular school.
Gently remind him (over and over) that the real goal here is on building a life. What does he want to do? He can still do that–when he gets going with Plan B.
There are a million ways to get from one coast to the other. So one highway closed–it will be ok and he will still get there.
I think this can be very hard for 17/18 year olds to comprehend, but they do comprehend it eventually.