(Alternatively, after you left the area, the Flood was repairing and re-using the combat forms you killed, and the Chief was just being attacked by the same couple hundred infected humans over and over again.) I mean, I guess Chief might feel better that he didn’t kill many of his people when he blew up the Autumn, but it’s still pretty horrifying that the Flood got pretty much everyone. Still, I was playing through the CE campaign on PC the other day, and it occurred to me that, with all the human combat forms you run across, most of the crew must’ve made it to the ring, and most of them must’ve been infected, which made me even sadder than I’d been knowing only a couple people survived at all.
Chief was just doing his own thing (maybe Cortana thought bringing in backup would just be giving the Flood more victims the Chief was the only one in an airtight, shielded suit). The novelization and the arcade game “Fireteam Raven” show there was an uninfected population of humans fighting elsewhere on Halo until the bitter end.
