There are literally hundreds of ways the world could end, some of which are very unlikely, although a few, sadly, are inevitable.
Now first of all, I'd like to say that I'm not religious, so I'm going to leave out the likes of the Rapture and various other religious theories.
First of all, our sun will eventually turn into a red giant, when it has consumed most of it's fuel, and will expand and most likely engulf the Earth. Could we escape to another planet? Perhaps, perhaps not, in my opinion, very unlikely.
We could also delve into anarchy, as suggested, and the human race could essentially destroy the planet. Likely? Yes. Escapable? Also, perhaps, perhaps not.
There are lots of other environmental or manmade factors which could alter the planet's lifespan. We could be struck by a very large asteroid, there could be a huge pandemic which kills us off, which isn't necessarily the end of earth, but could be the end of the human race/terrestrial life altogether.
There are probably countless more ways in which the planet could end, but I'll leave the rest to your imagination.