Many people believe that a hen will not let herself die on the nest. I myself believe they will. A friend of mine had a bantam hen that was always broody and determined to sit, but when she was sitting she flat out refused to get off her eggs, he had to offer her food and water, well one time his hen disappeared so he assumed she was setting somewhere, he never found her until he heard chicks peeping in the barn, when he found them the mother was dead on the nest.
Now of course I'm not saying that every hen out there will let themselves die, but I do believe it is possible to have a hen so determined that she dies trying.