Are the change fees less then the price of the ticket? If so just cancel his ticket and the extra funds above and beyond the change fee will be placed into a "holding account" for one year from date of purchase for most airlines that can be used on another flight for him.
If the change fees are higher then the price of the ticket, then if he is a no show, the entire ticket value will be forfeited and it should have no effect on the balance of the tickets (if they are booked on the same confirmation number, you might have to check him in, but he just won't board the plane).