Nothing will happen. If you really think about it, Earth isn't a old planet after all. Compared to some others ones. At least, What they have estimated. On Whatever day the world will "End" I will get up and yell out my house, Into my neighborhood, "So, The end of the world is AWESOME eh?"
Ok, Maybe I won't. But I certainly won't be sitting watching the "News" Seeing what will happen. I will be sitting where I am right now most likely, Playing TF2. Yes, Im serious.
Anyway, The world will come to no end. By the time it does, Everyone on this forum, will has passed away. We have nothing to worry about. Besides. Why worry about it when you can at least fulfill your life in case of that 0.01% chance it happens? I'd want to die happy. Not stressed out about the world ending.