It's a personal decision that only you can make. I'm not sure what corid is used for as I've never medicated any of my chickens. The thing I try to weigh out is, is it worth the suffering that the bird is going through? Will it recover fully, or have a poor quality of life if it lives? Will it need special treatment for the rest of its life? Can it be comfortable? Or, do I feel that the poor thing is going to die anyway, and am I just prolonging its suffering? Can you afford the time or money to baby a "special needs" chicken along?