From what I can tell with a little research, the Mormon position is quite different from what you suggest. Early Mormon polyandry (polygamous marriage with a woman having more than one husband) arose when a woman had been abandoned by an earlier husband, but not legally divorced. The Mormon church did not recognize the legitimacy of non-Mormon marriages, and allowed the woman to marry in the Mormon church, even though she had a legal and Christian husband to whom she had no current relationship. Her state of polyandry was legal and religious, but was not active, simultaneous polyandry. You can learn more at this link: "http://www.dialoguejournal.com/wp-content/uploads/..."
I have not researched Mormon end-of-the-world mythology, though one series of future fiction - The Folk of the Fringe, by Orson Scott Card - is influenced by it.
Be careful as you read - be aware of when you are looking at history, at hostile attacks in history, at rumor, and at scripture. Be sure to check out the history of Joseph Smith's church that did not go to Salt Lake - it tells quite a different story than the current Mormon church - though both do not do polygamy now.