I saw the movie with a group of friends, and after the movie ended, everyone was split on the ending. Half of us (including myself) thinks Batman died in the explosion, and the other half believed he lived.
I thought the scene at the end with Wayne and Selena was part of Alfred's imagination, because there's no way that Batman could have escaped that atomic bomb in 3 seconds over open water, as it was supposed to cover a 6 mile radius (I know it's a Batman flick, but Nolan doesn't like to pull "unrealistic" or fantasy magic tricks with Batman).
Batman dying with the bomb just makes perfect sense to the story. After living a completely miserable/meaningless life for the past 8 years, he realized that his only purpose in life is to be Batman. This time though, it's apparent that he's physically and mentally beaten to where he can't continue to be Batman any longer. In Dark Knight he said "Batman has no limits," and he "can't afford to know them," but he finally realized that he had been pushed to the limit.
The "life after Batman" that he wanted can't truly exist since Rachael died, Gotham (even though he saved it) is still in shambles, and his mind and body barely escaped Bane and Talia, as he was over matched in pretty much every way. As he was coasting over the open water with the bomb, I was just picturing him imagining all these things and realizing his fate was to die a hero.
As for the whole "auto-pilot" thing, I felt that was told to the audience to let us know that Batman had the option to get out of the plane with the auto-pilot feature, but he chose not to.
Just my thoughts. K I'm done. But wow, the movie was incredible. Loved it!