I hate saying this because it seems like such a cop-out, but as with many things associated with this surgery, the results vary.
For myself, I fully anticipated dealing with incontinence post op, particularly at night, which is the more common issue, as opposed to daytime incontinence...even bought adult diapers to wear to bed. Never needed them, and wound up donating them. I have had minor leakage when I have my occasional pouchitis, never any full blown incontinence. Within a week or two of surgery I could delay a bowel movement 2 hours or more. Within a couple of months, I went on a road trip of 6 hours, and did not need to stop any sooner than my car mates.
The main common complications are two-fold:
1. Those related to the immediate post op period, such as bleeding, obstructions, infection, blood clots, etc. Once you get past the first few weeks, most people do not revisit those (but some do have delayed or prolonged surgery related complications).
2. Those related to pouch adaptation and lifestyle adjustment to the neo-rectum. A few people sail through this and are happy campers immediately (especially those who do not have IBD). Most people have difficulty with loose stools, frequency, and even some urgency/cramping for the first 4-12 weeks. Some surgeons tend to downplay this, and the patient winds up feeling blind-sighted by it.
Early on, most of us will need to tinker with diet, avoiding most roughage, spicy foods, gas formers, sweets, alcohol, caffeine, etc, until the pouch has time to adapt and the gut adjust to the lack of a colon. Gradually, the body "knows" what it needs to do, and the small bowel learns to absorb water better. You can take bowel slowers and fiber supplements to slow and thicken output. Some surgeons are more liberal about this than others. Personally, if my surgeon told me I should wait to use them, I would have told him that HE should come over and clench my cheeks and keep the stool from trying to squirt out!! Fortunately, he had me on Imodium before discharge.
Unfortunately, the output is caustic and butt burn is common. That is why using a barrier cream right off the bat as a preventative is important. Butt burn is easier to prevent than treat. So slather on that diaper rash cream early and often, and you will not regret it.
Only a very small percentage never truly adapt and continue to be bowel cripples. Most often it is due to chronic pouchitis or Crohn's of the pouch. But, even those with those diagnoses usually find an acceptable functional level. Only about 10% wind up with failure and have their pouch decommissioned.
There is nothing wrong with choosing to stick with the ileostomy. Most people who do are just as satisfied as those who choose the j-pouch.
It is not all rainbows and unicorns, but it is not the end of the world either (at least 90% of the time)!
Hope for the best, but be prepared for the worst.
Jan