I give you that you have created an example that's difficult to answer, but
a) there are ways to solve this problem without killing someone (thus creating less suffering)
b) organ donations are very risky and it's far from safe you've rescued the other one
c) choosing the one "who should die" would be a hell of a task and I cant see anyone having the "expertise" to decide

Let's rephrase a scenario that's more sure, it's also a well-known one:
A plane with 100 people on board is hijacked by a terrorist, no way for the passengers to do something about it.
It's heading directly to a big nuclear plant or sky scraper, when it does there will be 1 million victims.
You have the option to shoot the plane or not to.
I would agree on shooting the plane, even when I'm on the plane (at least if I manage not to panic).
(I know a lot of people are gonna disagree with me on this one)