哈哈 okay, now serious. There is nothing that could destroy the planet and life on it in a matter of one year. no planet/asteroid, no unusual activities inside Earth. the global warming will last years too, and this surely wont cause the end of all lives.
Second, the Mayan Calendar is made before the leap 年 is made. Therefore, for the Mayans December 21, 2012 is already over. We've passed it (Mayans). If the leap 年 is not made, it should be mid-2013 由 now..