These are all campaign theories. I thought of adding a spoiler tag, but if you walked in here not playing Halo 4 already, it's your own fault. - Didact returns as infected, leading new horde of Flood from some other galaxy. - Good Forerunners follow Flood into galaxy with Chakas/Guilty Spark. They give Chief and Spartans upgrades. Causes another schism within the Elites/Covenant. - Space magic causes Cortana to come back to life, in a more corporeal form. ...yay.