I had the flap procedure and it didn't work. Prior to that I had a few draining setons. In fact, the first time I went in for the flap procedure I had such a bad infection that he ended up "cleaning it out" and giving me setons instead. Then I had to wait four months for things to heal better before he performed the procedure. When that didn't work, I had to take heavy duty antibiotics and then get another seton. All of these things did end up weakening my spinchter muscle causing incontinence at times. My GI wouldn't even consider biologics in my case.
My CR surgeon referred me to a surgeon that specialized in advanced gynecological surgeries. He was the best in his field in my area. He was able to repair my fistula, repair my perineum, and do a spinchter repair. He said I had so much scar tissue and I was "really messed up" down there. LoL. Adding to my problems, my perineum is already very thin and anatomically my rectum and vagina are very close together. My quality of life has DRASTICALLY improved. I now have very little incontinence, though it does happen ocassionally if my stool is very loose.
If biologics had been an option for me, I would have tried that first. I don't know why my GI was so set against it in my case. I had to have many procedures, setons, and surgeries to finally get RV fistula repaired.
I wish you luck.