I have no experience with FIP myself but I have read that cats can live with it and it doesn't have to be a death sentence. I know it is hard but as you said, Henry does seem to be improving.
Let me go find the article I read about it...(its around here somewhere...)
Here is a forum dedicated to owners of FIP cats:
http://www.atfreeforum.com/fip/" onclick="window.open(this.href);return false;
http://www.askthecatdoctor.com/feline-fip.html" onclick="window.open(this.href);return false;
What is the best way to care for a cat that has FIP?
There is currently no cure for FIP; therefore, the primary concern needs to be making the cat comfortable and deciding when to quit. Cortisone can help reduce inflammation and encourage appetite. Good nutrition, hydration and non-stressful environments are also important, but in almost all cases they serve only to prolong the inevitable. Therefore, we will encourage some owners to go with symptomatic treatment, but only if the animals are not suffering. There have been reports that the feline interferon omega is effective in combating FIP. We actually tested it against FIP years ago and it did not work. Fortunately, a double blind, placebo controlled study was recently reported from Europe on the use of interferon omega in treating FIP. Cats receiving this very expensive treatment fared no differently than placebo treated cats. This will hopefully stop the use of this treatment in the US and other countries, although some people still believe more in anecdotes than scientific trials. Unfortunately, veterinary medicine is filled with anecdotal treatments.
How do you know when to euthanize a cat that has FIP?
This is a decision only you can make, and it is a difficult one. I would never suggest euthanizing a cat, even with FIP, as long as it looks and acts fairly normal. Miracles do happen, but they can’t happen unless they are provided time to happen. However, I also cannot argue with those owners that decide to end suffering at an earlier stage, given the grave prognosis.
I always tell owners to decide to put an animal down when it no longer takes pleasure in life. But cats can feign health to the last moment and you often regret in retrospect not making the decision earlier. I did the same thing with one of my cats that was dying of cancer. He actually was dead one morning, even though I still thought he had time to live and seemed reasonably content. There is also a myth that if a cat is still purring that it is still enjoying life. But research has shown that cats purr even when in extreme pain, it is another way that they mask illness.
that is from here:
http://www.atfreeforum.com/fip/viewtopi ... mforum=fip" onclick="window.open(this.href);return false;
Unfortunatly I can't find the article I was sure I had read but I'll keep looking for it..