Mites/lice will pull birds down and yes, can eventually lead to death. I'd suggest getting something along the lines of DE, Sevindust, Adam's flea and tick spray, or even Ivomectin (in whatever form, it is a wormer that takes care of lice, you can find it in the cattle section of a Co-op/TSC; pour-on is pretty cheap, apply 1 drop out of a ear/eye dropper per 2 pounds or get the kind that can be given orally and apply 5-7 drops per large fowl 3-5 drops per bantam/small bird down the throat). It would probably be wise as well to treat the coop/roosts for lice as well using a oil substance (vegetable oil would probably work, skin so soft, etc). There is also a dip that can be applied to the bird or used in a sprayer sold at TSC/Co-op's to treat the area and the bird's fairly cheaply.. I think it's made by Martin's, we have their dip for dogs that takes care of fleas, ticks, and mange.