Max had pancreatitis a couple of years ago (and it was TERRIBLE and he had to spend the weekend in the hospital on IV's)...he never had diarrhea (at least not at home) but he wouldn't touch food and just kept vomitiing white frothy stuff. It was just awful!
When he got home, the vet put him on Hill's W/D and he's been on it ever since; I think he'd been on Royal Canin first (along with some Cesar's which he loved), and I think he wasn't too excited about the W/D at first, but it didn't really take him too long to get used to it. Now I give him the canned twice a day as his normal feeding and use the dry in between when he gets his "snacks"....Max is not really a picky eater at all though. And he's always wanting something to eat, so I thought it would be good for him to have SOME of the dry food, so that's why he gets a few as a 'Snack" or treat in between meals. I figured it was safer than giving him other treats, although sometimes he gets apple.
I think the main thing is to keep them away from rich or high fat foods. Things that would aggravate the pancreas or make it work harder (so anything that would require more insulin production to digest).
The W/D supposedly has more fiber in it which is supposed to make them feel fuller, but I sure don't notice that with Max
...he's perpetually looking for food!
Good luck with your little one. I know how scary it is to go thru that and not know what's going on~ our episode was a true nightmare, but thank goodness, it turned out ok!