Several of the things that happened for me after bypass - GERD is gone. I had developed Barretts esophagitis with a precancerous Barretts polyp. All that is resolved now. (Polyp was removed of course), but all evidence of Barretts has now vanished. With the GERD gone, my asthma is also gone. I had no idea of the relationship between obesity and asthma. And my sleep apnea is gone - no more Cpap needed.
Prior to surgery I was taking Aleve twice a day for arthritic pain. I already had gotten one knee replacement and the other was in pretty bad shape, as well. I did not know a day without pain. Since bypass, I have not used any NSAIDS and I have NO PAIN. My knees, back, and hips do not hurt. Unbelievable. Adipose tissue releases all kinds of inflammatory cytokines and I was surprised at how quickly the inflammation and pain resolved. I was able to greatly increase my exercise and finished a triathlon just 8 months after surgery and a 50 mile bike race a month later. No NSAIDS needed! I am presently training for a 100 mile bike race, another tri, and a rim-to-rim hike of the Grand Canyon. More energy that I know what to do with.
As far as malabsorption goes, I do have fat malabsorption. It just goes right on through. My vitamin levels are fine except for vitamin D, so I am on extra doses to keep that up. From what I have read, the lower parts of the small intestine will eventually start taking on a more absorptive role, so it will be interesting to see how that plays out for me in the future.
Complications for me included some blood clots in my legs a week after surgery, even though I was walking within hours of surgery and was doing 10,000 steps by the end of the first week. It's just something that can happen with any surgery, especially in an obese patient. I also developed an ulcer about 6 months out. Both conditions easily treatable and resolved with medication.
I hope this offers some light on your specific concerns. I think the biggest thing is to have a positive mind set and realize that this surgery offers you a whole new life if you are willing to seize it. There will be ups and downs, and you have to focus on the ups and learn from the downs.