It looks like the cat was bitten by something bigger than him.
So far, the prognosis is that "he should live" but that is not guaranteed. The doctor apparently fixed whatever was wrong with surgery, including removing a large amount of pus from his abdomen. From what I have learned, he basically opened him up, rinsed out his abdomen (stomach cavity) and fixed all the tears and holes in his flesh.
To be honest, I never knew he was feeling bad. He was outside as usual, and came home the next day. I thought that is what cats do. Anyway, I guess either Bridget or Maryann were messing with him and noticed something amiss. Next thing I know, I am getting text'd at work saying they were immediately taking him to the vet.
Now, we currently have a cat. He is fine, rather punctured and shaved, but he is alive. As a general rule, I rather dislike cats as a whole. This one is different. He is more like a thing, than a cat. While at our last house, he caught and disposed of all the mice in the area. This included all intruding mice into the basement. So, I really do think that he 'earned' his keep then. There was no reason to not bring him along. He earned it there and he can do whatever he wants until we need him again.
I do think that him being a cat, he probably would have been good for the new owners too. But I like him and he has some strange attachment to me. I just hope he survives this problem. Like I said, the prognosis is good.