With one of the first hard bellies we had i talked to another breeder and he said help them pass it as soon as possible. I did try warm soaks and different hydrating methods to no prevail. I found that the longer they sit with the hard mass the less likley they are to come back around. The longer it stayed the worse they got and i have never seen one actually pass it. We just slowly worked the mass out very carfeully, it can be a long process and very tidious. After it has been passed with "assistance" about half of them have lived, the other half did pass away, wether it be stress or internal damage or something else i am not sure, but the ones who started eating and drinking did fine afterwards and had a 100% turn around, the others just faded till there was nothing that could be done.
I have talked to numerous breeders afterwards about the subject and i have gotten the same responses. They have also had about a 50% survival rate but if the hard mass isnt passed then their hasnt been any that i know of that have survived, so i guess a 50% chance is better then none at all.
I have only had to do about 15 max in total and all of them came into my care that way. I have never had one develop a hard belly once set up. There may be a way of preventing it but i am not 100% sure, i have never seen it happen in any of our CB. Like others have said i believe it is a combination between the yolk sak and possibly dehydration.
Hope that some of this helps.
Thanks Kim