Special thanks to OldTimeGator - We followed your advice and duckling doing well. Had added complication of humity has been wrong in incubator and umbilical was also large but we tied it off and snipped and no bleed. Also fed with Life guard mulit vits and little thing is pepping right up running round brooder. Very time consuming to care for very sick chick but worth the effort when your not a commerical venture, and have the time. It was a long shot but we got lucky - thanks.
It could make it but realisticly it probably wont. If it were me I'd cull it now.
You guys would have killed about 5 of the healthy chickens I have running about and several button quail. I've had lots of chicks hatch and pop out of their shell a bit early. The quail commonly do it. I've had many with yolk still attached. About 3 have died but more have survived. Just leaving them in the incubator is usually enough to let them finish absorbing and then they act like every other chick. You just have to keep the yolk sac from rupturing before it's absorbed which is why I wrap them well in a damp paper towel.
I am so glad i just read this post. I had a chick hatch this morning with the egg sack still attached. The chick is tiny but seems to be doing ok. I have wrapped it in a wet paper towel in the incubator. I'm hoping it survives. Another one of the same batch hatched also, very large and healthy. I'm just gonna wait and take my chances it will survive.