If he is able to bathe regularly, mites should not be an issue. He's probably not interested in it but I would offer some water to bathe in. A large litter pan, a flat 3 gallon feed pan or even fill the tub with a few inches of water and see. Put him in a wire crate and place it on the lawn Grass is their natural diet. You are getting to a critical time where he does need to eat. 4-5 days is as long as i would let him go. Throw his food in a blender and syringe feed him if you have to. I agree that his mate will help him. You could take him out to the barn and see if she can get him to eat. Take an old t shirt. Put the head through an arm hole, cut holes for the legs and gather the rest and tie it up on his back.