Congrats to your son on his achievements. I know it can be rough getting colleges to understand and work around such a commitment (other than a few schools in a particular geographic region).
Most of the missionaries I know have decided to return early. I know that’s not what they planned, but it seems to happen pretty often. Is your son super-excited about his call or do you have a sense that he may come back before 2 years? Does he want to consider asking for the standard college 1-year deferment just in case?
Hope it all goes well!