At what point is an unhatched chick viable?

I had a couple silkies sitting on eggs this summer and unfortunately one of my wyandottes got loose from the other flock, rousted up the silkie hens and raided all the nests. All eggs were a loss except for one which was broken open and there was an almost ready to hatch chick. I'm unsure as to how many days they were away from hatching, as I just let the silkies do their own thing and check and candle periodically. The chick had it's eyes open, it was very groggy and cold but it was alive. It was still sitting in about half of what was left of the shell and there was a small amount of yolk still left in the shell as well. In the time it took to scramble to assemble my incubator set up to attempt to save it, it did end up dying, but I want to know for my own curiosity,

should anything like this ever happen again---is it even worth trying to save a chick at that point if it is still attached to some yolk? I have successfully taped a cracked shell back together and saved chicks that way but they did hatch w/in a couple days too so they were pretty much thoroughly cooked anyway, but I've never attempted to save one this early. At what point is it futile vs. when is it possible?

Well, I guess you never know until you try! My personal opinion is, if it's that early it probably isn't going to make it anyway. But, if you have the time and resources to give it a shot, what's the worst that could happen? The chick would die. It's going to die anyway if you don't try.