After the egg forms, if the hen is dissatisfied with her choices of where to lay the egg, can she reabsorb the egg, or is it unstoppable once armed?
My suspicion would be to say 'no' because if that was the case, egg bound hens would eventually get over it and just reabsorb the egg. I'm guessing that once it is coated with the shell, it's 'go' time and the hen may be able to retain it for a little while until she finds the right spot or feels safe, etc to lay it, but at some point it has to come out or she will have a blockage and eventually die.