Answering as someone who has never BEEN in such a situation,
which of course is the only way to know what you'd really do:
0. Questions: can you eat parts of people and not have to kill the person?
can you wait for someone to die of natural causes?
In general, I would seek to respect the beliefs of all the people in the group.
1. If one person agreed to be sacrificed, or if all the people agreed to draw straws, etc. where people at least had time to be prepare mentally and not be rushed to do things against their nature, then if this were necessary, I might be OK with that under if everyone were at peace. I believe if it is really God's will, then you can come to peace with it in advance.
2. If anyone is going to suffer and not be OK with that, where the group decides it is better to die together than kill one of them against their will, I'd respect that also. I am guessing that since I tend toward this way of thinking, where I'd rather die before i have to do something weird or sick in order to live, then I might end up being the sacrifice bunt.
3. In the case of St. Maximilian, before he was sainted of course, he offered to trade places with a prisoner who was chosen for execution; because the other man had a family. So if someone agrees to that, I believe that would minimalize the suffering.
Overall, I would not want to put people in a position where they have to falsely justify something sick in there minds in order to explain the choices that were made. I worry that makes people mentally ill to force them into denial and rationalization. So if there is any way to avoid that, I would. For life to be worth living, the quality of life is important, too and I would not want to make people crazy, having to live with that decision for the rest of their lives.So I would prefer the decision be made by consent where people agree to any sacrifice.
If they don't agree to have someone killed, can the group wait until the first person dies of natural causes or asks to be put to death? Can they all agree to take turns sacrificing parts of their bodies that can be eaten without killing anyone?
PART ONE: THE MORAL SIDE OF MURDER
If you had to choose between (1) killing one person to save the lives of five others and (2) doing nothing even though you knew that five people would die right before your eyes if you did nothing—what would you do? What would be the right thing to do? Thats the hypothetical scenario Professor Michael Sandel uses to launch his course on moral reasoning. After the majority of students votes for killing the one person in order to save the lives of five others, Sandel presents three similar moral conundrums—each one artfully designed to make the decision more difficult. As students stand up to defend their conflicting choices, it becomes clear that the assumptions behind our moral reasoning are often contradictory, and the question of what is right and what is wrong is not always black and white.
PART TWO: THE CASE FOR CANNIBALISM
Sandel introduces the principles of utilitarian philosopher, Jeremy Bentham, with a famous nineteenth century legal case involving a shipwrecked crew of four. After nineteen days lost at sea, the captain decides to kill the weakest amongst them, the young cabin boy, so that the rest can feed on his blood and body to survive. The case sets up a classroom debate about the moral validity of utilitarianism—and its doctrine that the right thing to do is whatever produces "the greatest good for the greatest number."
[ame=http://youtu.be/kBdfcR-8hEY]Justice: What's The Right Thing To Do? Episode 01 "THE MORAL SIDE OF MURDER" - YouTube[/ame]
There is a series of these lectures in case anyone is interested
Don't forget what is spiritually good for people counts also, not just what saves physical lives.