I have never dealt with this problem in a dog before, but I have IBD (Crohn's Disease). I've had it for close to 30 years, so I could tell you my own experiences if you think that will help at all.
I also used to talk to a woman online who has Crohn's, and she had a cat who also had it. The cat would have times of remission where he didn't have symptoms and did very well. He had other times when he had to be on medication and eat a special diet. I haven't talked to her in a long time, but her cat lived a pretty normal life and was about 10 years old at the time.
