Hello Mike, I'm Dr. Bob.
I'm sorry to read of your hen's death.
There are two different conditions that can cause eggs to drop into the abdomen. Internal laying and false laying are the common terms for these conditions, and neither is treatable, unfortunately.
Internal laying is caused by the peristaltic action in the oviduct reversing for some unknown reason, causing the eggs to be propelled back up the oviduct, and out into the abdominal cavity. False laying is caused when the funnel shaped opening of the oviduct is damaged, often by a respiratory virus infection when younger. The egg then cannot gain entrance into the oviduct and drops into the abdominal cavity. These eggs can lay harmlessly in the abdomen until a bacteria, Proteus is a common offender, gains access to the retained egg materials and a condition called "yolk peritonitis" occurs.
Unfortunately, this is practically always fatal. In valuable zoo specimens, surgery is sometimes attempted to clean out the egg material and remove the reproductive tract, but chances of success even after this expensive approach, are rarely favorable.
If you should have further questions, please let me know.