Appx what percentage develop a stricture after surgery 4 colon/bladder fistula & diverticulitis? Is the balloon treatment (dillation?)very successful?

Not frequent. If stricture develops may be due to recurrences of disease, balloon dilation may help, will require resection for better out come.
Not often. To be honest in 14 years of doing this operating I have seen, maybe one stricture and yes balloon treatment can be effective depending on severity of the stricture and length. The other question is the trimming for the stricture. How log after surgery. If it was immediate after surgery then this is a technical issue and not scarring.