Yeah but if you think about it, at the end of 4, you would of thought it was done. Cortana died, he saved earth and such. And by the way he took off his armour, I just thought he gave up, or just to be 'human' again instead of being a 'machine'. He looked pretty old and I don't honestly think his going to last in the new halo because of new and improved Spartans ( maybe there called guardians now ).