It's not a matter of question, if it will happen... but when. There are so many possible global destruction that could literally happen any second and it's happened many times already. Definitely not science-fiction anymore. Some possibilities include: nuclear war, super volcano (anytime now yellowstone...), gamma ray burst, starvation, aliens, global warming, solar flare, supernova, asteroid, rogue black hole, artificial intelligence revolution, biotech disaster, magnetical reversal/spinning off axis, worldwide colony collapse (honeybees), deadly plague, mass insanity, and the list goes on.
So... when is it our time?
Let me remind you we've only been on this earth for a very small fraction of its time here.