My Faraday theory: Daniel could not stand to be at the Dharma camp with little Charlotte so he left. If you recall, Charlotte left the island at a very young age so I think that Daniel comes back after little Charlotte has left. We know he didn't kill himself because Desmond visited him in the future in the episode 'The Constant' (my favorite episode!).
May I also say that Sawyer is looking damn fine all cleaned up! *sigh*
And yes, there are a number of years left until Ben kills everyone because there are still Dharma stations to build so I am sure that everyone will move back to the future before Ben kills everyone.
I like how Ben gets beat up all of the time

. Has there ever been a TV character that gets a good beat down almost every episode??? I think it must be a record of some sort!