I have had quite a few with pancreatitis over the years...my own and fosters. Usually they are hospitalized for 3 or 4 days for IV fluids and then are sent home on I/D. You will have people advise you against this food, but it has never failed for me. And, right now, I would not try to change it.
Sometimes it takes a week or so for them to totally improve. Just don't give him anything else to eat! They need time for their little tummies to settle down.
Yes, many bouts of pancreatitis are started by food, but many are really from unknown causes. I never heard of stuffing from a toy causing it, but I suppose anything is possible. You said that a treat made him sick....was this type of treat given to him before the initial illness? Maybe it is the problem?
Here is a link with some good information:
http://www.peteducation.com/article....2+1580&aid=335