It really depends on the person, and you would know him better than anyone here, but if nothing else just go with the usual sort of thing, just say something like you're sorry and you'll be thinking of/praying for him and that you're there if he needs anyone to talk to. Then give him some space and if he wants to contact you again about it he will.
I hope you won't expect the thread to walk you through every interaction with the guy though, like I said, you would know him best.