Thank you all for your support. I'm still upset, but getting there. Sometimes I'm wondering if I hadn't tube fed him he would have experienced none of the stress (which I think pushed him along) but then since he wasn't eating at all would he had pulled through?
My other duck is still hanging on. She stopped eating and she is wasting away but trying to tube feed her would definitely kill her because she's not used to be handled at all. We didn't hatch her. So I pumped her water with all sorts: electrolytes, poultry vitamins, charcoal and brewer's yeast and a handful of pellets that go mushy in the bottom... just in case... I change this everyday. She's not compulsively drinking anymore, just normal drinking, and this morning all 4 (surviving) ducks had a warm bath with epsom salts and she was so happy. She even tried to beat her wings but her balance is no good. Also managed to preen a bit but she can't reach her tail feathers. Finally she ate a bit of coriander that I dropped in the water... so fingers crossed...