I'm very sorry for your loss. It is never an easy decision. :hugs
When I necropsy a bird, I'm very grateful for the information they provide that may help one of the flock in the future. Any knowledge they provide is like their last gift to me. But it's always hard.
I hope you get answers...
Hens with swollen abdomens generally don't recover. It could be ascites or it could be infectious material. Having said that, depending on what's going on, some of them can live for a while. If you think it may be viral, then getting a necropsy is a valid thing to do. And the results can...