My (late) vote is:

The charismatic but otherwise underqualified person(s) who attempts to to seize control and create an empire for themselves amidst the confusion.

They make a series of 'calculated risks', and they cull those individuals they feel 'have no place in the new world', but they inadvertently cull those individuals who merely piss them off or who they have the most difficult time getting along with. The community is momentarily reassured, continues to drink the underqualified Leader's guidance kool-aid, and blame - as instructed to - those who were culled for any hardships the community (or communities) may endure.

But eventually, after the body count has reached staggering highs, people realize all too late that they placed their lot in with the wrong leader(s) and had a hand in what might eventually prove the end of mankind.

Insert "Five Stages of Grief" (and all the drama that ensues from everybody going through it and most handling it poorly), and in the end they die off, giving way to those individuals who found a way to resolve their differences without destroying themselves from the inside out.

That is a lot of planning. Most people are too lazy to make that much effort. They just tend to lose it or blame someone else for all their woes.

But it is an interesting idea. Kind of a Jim Jones kind of vibe.