I just wrote a 12 page research paper on nuclear weaponry. Right now the United States has over 7,000 nukes in our arsenal. The only other country with anywhere near that is Russia with 6,000. Since the Cold War ended, the tension between the United States and Russia has eased sufficiently, and treaties have been signed. These two countries will not get into WWIII with eachother. The only other possibility are the "unknown" countries like Iran and North Korea, and the only evidence anyone has as to their possesion status is that they were looking to obtain materials and plans used to create the devices. If they were able to manufacture the bombs, they would be able to use it once on anybody before the United States or Russia stepped in and nuked them to hell with their endless arsenal. Pakistan, India, South Africa, Brittain, France and China are the only other counries to have bombs. HOWEVER, South Africa recently dismantled theirs in an effor toward world peace; Pakistan, India, and Brittain are all allies of the United States; and everyone knows France will surrender their bombs before they use them, because thats what the French do. China is the only counrty known to have nuclear weapons that would possibly use them against another country, but the thing is, is they have no motive. If they did try to though, all of the allid countries with nukes, numbering around 15,000 nukes total would destroy China at their first opportunity.
So to answer you question; The world may very well end because of a nuclear war, but it will not be any time soon. I too have heard teh prophecy of the end of the world in 2012, but I did not hear any reason associated with it. It was also a prophecy that the world would end on y2k, but that never happened, so i think there is nothing to worry about.