Well, first of all, Warren Jeffs was right about the end of the world happening on December 31. It's just that it was an invisible end of the world. The rest of the world is simply confused and doesn't know everything has ended.
Seriously, the FLDS is very loosely based on the LDS (Mormon) church. After the LDS church was established, though, a quorum of twelve apostles was established that was equal in authority to the first presidency, which consists of three lay apostles. Subsequent to that, a quorum of Seventy was established equal in authority to the previous two quorums. This organizational structure effectively kept one person from seizing control and running the church as a dictator. If revelation is received, it comes through the First Presidency; and when the president dies, the First Presidency is disorganized and the Quorum of the Twelve becomes the governing body until a new presidency can be established.
What Warren Jeffs did was establish his own Quorum of the Twelve (which has only several members) and then name himself as the sole authority of the church, overriding all existing authorities and all previous authorities. Before Jeffs, his father instituted the one-man rule, but many suspect Warren of being the mastermind. And though many accept everything Jeffs says as the gospel truth, the church's doctrines are so adverse to suicide that I doubt anyone in the church would go that far. They may arm themselves and fight the government until the last man, woman and child, but Warren Jeffs is so nuts that I doubt that his church will survive. If anything, some other leader will arise and claim to be Jeff's successor. I imagine that if a disaster happened and they ended up killing themselves that, yes, the Jehovah's Witnesses would take advantage of it, but only in context of the signs of the times.