Diatemacous earth sprinkled on him should help get rid of the mites, I think, just try to keep the dust cloud down. If money's no object, find a vet to operate on your bird's neck. If he's suffering, as hard as it will be for you, I'd put him down. He was obviously well loved and has had a good life. If the hole is just like a hole in a tube and isn't obstructed by "moving parts" and what-not, I wouldn't think it'd be very complicated for a vet to slice open the skin, stitch the hole closed and patch him up. If you know where the hole is and you had someone wrap him up in a towel and hold him good, you could probably do it at home yourself, but I suspect you're too emotionally involved to do that yourself. And if he didn't recover, you'd have a hard time reconciling what you did even though you were trying your best to help him. If you've got a good vet school near you, try there. Sometimes they'll operate on animals for free, especially if there's research value there, as in, how'd this duck get a hole in his trachea? We have two very good vet programs near us and I hear they do stuff like that all the time. Best of luck to you and Aflac. Hope things turn out well! 
