Humans are just so fascinating...

All jokes aside, Gabriel would do every single thing in his power and then some to try and get out of it. Goes through all five stages of grief and then some, threatens to kill people, all that good stuff. Madison I'm sure wouldn't feel too great about a surgery either, but she understands it's medically necessary. Of course, Gabriel would be extremely reluctant towards surgery unless it's literally life or death, but even then he'd still try to beg and terrorize Madison out of it. Best shot would be to somehow sneak up on them from the side (not even from behind because Gabriel would be there) and knock them out with a tranquillizer or some anesthesia. Which, of course, would only traumatize them more, but ya got to do what ya got to do, I suppose. At least Madison would try not letting Gabriel rampage too hard afterwards, ahahaha.