The dr is right.
His diet should be about what anyone with an IBS should eat. Primal is really good for that. You want less inflammation. Obviously he should take notes and eliminate things that cause a problem.
I don't know what size the opening is, but you wouldn't want him to eat things that can get trapped in there and ferment, like sesame seeds, sunflower seeds, etc. The high fiber recommendation is to keep things moving and "swept" inside.
If he has to get the surgery, do it. Fighting a problem like that robs energy all the time. When the problem is removed, it's like getting a jolt of energy.
I don't have a colon at all anymore. Due to colitis, the whole thing had to come out 20 years ago. They replaced it with a j-pouch made from small intestine. It worked out really well overall, but in Dec it developed a small opening a lot like diverticulitis, but in a different place. I have been back and forth to the dr all year about it and just had a surgery last Weds to close it. It's been a tough year, some of the things we tried first didn't work out. I had some trial and error for a few months as far as knowing when it was flaring up and I needed to call the doc.
Your husband will probably need to also learn when the pain indicates time to reach for the anti-biotics. Mine would flare up even before I got a fever. One time I went to the emergency room, said it was flared up, and they said "you dont have a fever and your white cell count is OK." I was back in the emergency room the very next day. The tests didn't pick it up fast enough.