Hopefully you'll never have to deal with something like this, but it sounds like you have some great support if you do. I'm not sure what causes hard belly, but at least for me it didn't have anything to do with emerging from the egg early, so I suppose it can happen to anyone.
I think I was fortunate in that I didn't wait too long before reacting. I was tempted to let nature take its course and see if the snake would eventually absorb some of the hard yolk, but I didn't think it would and wanted to proceed before the snake became too weak to survive the surgery.