How did Master Chief die?

Answer 1

It appears at the end of the final mission that he and Cortana were killed when Halo was fired before it was ready - the blast that destroyed the Flood also destroyed their frigate at the end of Halo 3.

But, if you are one of those people who actually sit through the end credits of a video game, you'd know that there's a secret video, proving that both Master Chief and Cortana are alive.