In Halo 3 it kinda sets it up as the hero goes as he enters type deal, like, in Halo 1, you awaken from cryo sleep, and at the end of Halo 3 (SPOILER!!!) Chief goes back into cryo sleep.
There will be more Halo games no doubt, but yeah, MC is done...
They should make a Halo where you get to be an Elite, not like Halo 2, but as in you be the same Elite throughout the entire game, I think that would be kinda awesome...