the Mayans were a lot more knowledgeable about astronomy than we are and that's when they ended their calender for this world, they also believed that we are the fourth (if memory serves) incarnation of the world, which lines up with the mass extinctions we know of, I really don't know what will happen maybe they just got tired of making entries on their calender, I have no idea of why people are so interested in figguring out when the world will end either. There is not a lot we can do about it either way so we will just have to wait and see what happens.