Is this a reasonable approach? I'm really not sure. Perhaps, if test results show pancreatitis and absolutely no treatment works. (You are not there yet. So much hasn't been done yet.) Otherwise I would want to work on resolving the problem without a feeding tube. It can be done. Also, you might want to keep in mind that a PEG tube can cause esophagitis. If that happens, it's just one more problem that needs to be dealt with. And the medications required to treat it work against everything you're trying to accomplish.
It will be important for you to see the blood work results and I urge you to ask for copies of all the results for yourself. I can't emphasize how important that is.
I'd like to ask you, what are you feeding, is it canned or dry, and what kind of changes have you made, what kind of different foods have you offered since your kitty has lost his appetite? Are you leaving out food, or are you trying to keep a feeding schedule? Have you tried offering all-meat baby foods? What about kitten food? Have you tried any? What about home cooked chicken breast without the skin, etc? And what about prescription food, Hill's a/d for instance? That's good, even if a cat has pancreatitis. (In fact I remember a kitty that actually recovered from pancreatitis with the help of this food.)
Fish is one kind of food I would not offer in any form in this situation.
I'll be honest with you, I would do everything in my power to avoid having to use a feeding tube. As long as the liver is functioning normally, any underlying condition can be treated with the appropriate medications. And the right treatment brings back the appetite. Also, since vaccinations cause inflammatory responses, which in turn can lead to a list of complications, including pancreatitis, it would make sense to deal with this situation holistically as well, in addition to any necessary conventional treatment. I'm thinking, since holistic vets know a whole lot about dealing with vaccination related serious complications, I would want to see one to get some help.
One place you might want to look:
http://www.holisticvetlist.com/
Go to advanced search.
You might also Google holistic vets in your area.
This article is good reading, it explains some things
http://www.dogsadversereactions.com/...ineDamage.html