Update

Hershey is home. He stayed at the vet for four days on an IV to re-hydrate him. He did not "get over it" as the doctor hoped he would. He is in line for a kidney transplant (which I was surprised to find they actually do in cats), but he may not make the cut because he is on the borderline of being too old (he's fourteen). While we wait for an answer from the transplant people, he is at home on many different medications, but still not doing very well. He's weak and can hardly walk on his own. The doctor says if the transplant doesn't work out, he probably has a few weeks max to live. He's had a good long life for a cat, and I'd rather not have him suffer.

...but I don't want him to leave.