First, the Aliens will send a meteor infected with the zombie virus crashing into earth. The ensuing CIO/CC & BF/FF debate will lead to one infected BnB member biting another, hence starting the zombie apocalypse. A massive tsunami will wash away most of the zombies, but all the world's leaders will retreat into their mountain shelters to survive the extreme weather. Food and clean fresh water will be in short supply, leading the major world powers to bring themselves into a standoff not unlike the Cuban missile crisis. Kim Jong Il/Sung/whoever the fuck is currently the Dear Leader of North Korea will seize the opportunity to show off his world dominance by pressing the big red button and the world will be imploded by nuclear war and eliminated from the universe.
Thank goodness, because 7 billion lives are a small price to pay to eliminate the Kardashians from this planet.
Sorry, I've been up since 3:55am and he finally went to sleep. Now I'm bored.