You may want to move the pair into the house to keep the flies off him if you can't put them into a screened area. If his Missus keeps picking at his bandages, maybe separate crates right next to each other would work.
My lone surviving duck, Lucy, has been indoors since I found her the day after the attack. I have been fortunate that we haven't had a maggot problem, but her scabs are now sloughing off and leaving skinless patches on her, I use really sharp small scissors (embroidery scissors will work) to cut off dead patches of skin. You can sharpen them by cutting a piece of aluminum foil a bunch of times before you use them. Check them on a piece of kleenex for sharpness.
You may need someone to hold your drake while you trim his feathers and necrotic skin. He may allow you to do it or he may want to 'bite' you. Let him- it gets out his frustration and won't injure you. I usually have my husband hold her and drape a towel over her and let the part I'm working on stick out. It helps keep her calm.
Once you remove the dead tissue and clean the wound so there are no more maggots/eggs, then pack it with antibiotic ointment wihtout pain reliever (at least without any "caine" pain reliever.) My duck's worst injuries were on her head, so I couldn't wrap them (a gash between her eyes and down the side of her bill, you could see some bone - and a bunch of bites on top of her head just before her crest).
Maybe you could use a vet wrap in a color close to your drake's natural coloring to hopefully prevent the picking. Although my duck didn't bother her leg bandages and they were bright blue painter's tape over kleenex bandages. I read on here somewhere to use unscented regular kleenex (not the soft linty stuff) as a bandage instead of gauze because it is easier to remove tissue stuck in a scab or wound than the gauze fibers. It has worked for me so far. Although I find gauze pads are better to use for debridement if you must keep a puncture wound open.
I board my chickens at a small farm, and the woman who lives there uses Scarlet Oil on all her poultry wounds. Even if there is a big patch of skin missing, she sprays the wound down good and lets the bird go. It has worked for her. The birds healed, but had minor issues. She never had any head wounds - just neck or leg wounds that earned those 2 birds the monickers "Leggy" (who walked with a straight leg) and "Necky" (whose neck is forever bald) - LOL. Since Lucy had head wounds, I chose more conventional treatment.
As far as the drake is not eating. Lucy didn't eat the first day after her attack, Just drank water. I added poly visol without iron and bite homeopathic to her water and offered her favorite food on earth - green peas, She refused all forms of food whether it was crumbles or pellets, wet or dry or anything else and lived on green peas for a week and a half before she would even look at pellets. I think her bill hurt too much. It had been chewed on by the nasty scary thing that tried to kill her. Sometimes when she ate, it looked like her bill moved independently of her head. I don't know if that is normal, but I let her have what she wanted. I figured, if she lived, she will get better. If she died, at least she had what she wanted and I tried.
The skin on her bill is still rough and peeling, and she has a hole on the edge, but she is eating anything she wants, now, and digs in the mud.
Keep posting here with your questions, Somebody will have suggestions eventually. If you want to read everything I did for Lucy, it's on the duck forum and called How Lucy Got Her Groove Back.
