Kidneys. Getting a transplant would suck, but it’s at least possible. I’ve got siblings I could get drunk and leave in a bathtub full of ice, if nothing else.
I’d take the shiny new legs. Hell, I could stand to lose a few pounds- take 'em.
Pun intended.
Legs-then I’d sue the living SHIT out of said doctor. (Besides, I could hide my stumps with long pretty skirts in a wheelchair)
Kidneys-I’m O neg. I’m the universal donor, so I’d have to wait until I could find someone with the exact same blood type. 
I choose scenario 2. Since I’ve already had my left kidney removed, as soon as I got the diagnosis, I’d just switch doctors, cuz the one telling me that would obviously be imcompetent. 
On further reflection, I’d definitely keep the kidneys, unless I was assured of a perfect transplant match (which is not currently possible, so far as I know). Dealing with anti-rejection drugs and associated complications does not sound very pleasant.
Firstly, the word is debriding.
Secondly, what do you mean by “wear a bag”? What do you think the kidneys do?
I thought it might be a cute way to describe trousers with no leg holes (i.e. the leg option), but I’m interested to hear Omegaman’s explanation too.