So... has anyone ever had a duckling hatch early with its yolk sac still attached?
If so, what are the chances of one surviving?
I have never hatched ducklings so I have no idea. A fast search showed several threads of ducklings that did hatch with the yolk sac attached and they survived. Try posting in the duck section.
Here's a link to the ducks https://www.backyardchickens.com/f/42/ducks