I'm so sorry. It's a tough decision but it sounds it was the best thing for him.
I wasn't going to say this before, because of being not really helpful and a 'downer', but the one dog I knew some years ago with perianal fistulas had ongoing problems for, wow, probably several years, was in significant pain much of the time, his owner tried EVERY POSSIBLE THING, finally surgery, then the surgery caused nerve damage that resulted in permanent loss of control of that sphincter, dog was ultimately put down. I am sure there are good stories of recovery, too, but at least, seeing what this co-worker went thru with his dog, I think you were absolutely right to take the magnitude of the condition seriously.
Big hug,
Pat