What happens to the chief in Halo 3?

After Halo 3, you believe that Master Chief and Cortana did not escape the explosion of Halo fast enough. However, if you beat the game on legendary, you find out that although they warped away fast enough, half of the Dawn was destroyed, and they are floating in the middle of space. Master Chief enters a cryogenic chamber to stay alive, and as the video ends, you see the wreckage drift towrds a new, mysterious planet (perhaps a halo 4?).