I had a second surgery because the surgeon "forgot" to put back the small intestine after removing the gallbladder (it happened to slip out a bit when he removed the bladder through a small hole below my belly button).
When I came back in again, throwing up dark green bile, the new surgeon said that it was possible that the intestine was beginning to die due to being glued to the surgery wound, because it would lack blood circulation from being folded.
Luckely, it all went well and my intestine survived.
This is medical malpractice and it sounds as if that goes for your dad as well. I might add that I am in the uk as well and I am suing nhs for this mistake. It's been a nightmare and I won't let them get away with it.
C.