If he has a legitimate medial issue/reason on why he can't fly and can produce a Dr's note, I thought they would usually allow you to cancel and get a refund? Doesn't hurt to try and/or call a rep to see if that is an option.
And yes, cancel if you plan to use the unused fund less the fee. Otherwise (if the fees is more than the cost of the ticket), just hold off and see if you can get a refund through scheduling changes for the flights.
Good luck!