if going by biblical prophecy i think the movie "this is the end" depicted what may happen.
other end of days scenarios that are believable or somewhat believable.

1. fanem on a global scale brought on by an environmental disaster.
2. eruption of a supervolcano that spews out ash and toxic gases that fill the sky making the air unbreathable as well as blocking out all light from the sun.
3. an uncontainable viral outbreak that is resistant to treatments with a lethality rate of 99%
4. collision with a massive non terrestrial object such as an asteroid.
5. nuclear war