Halo season 2's Fall of Reach aftermath differs. After the Covenant attacked and glassed the UNSC fortress planet, the Human-Covenant War is concluding as both sides search for the first Halo ring.
In order to avert panic, Fleet High Command suppressed the invasion's impending arrival. Halo's core canon says this killed many and devastated Reach. Halo season 2, episode 5 ("Aleria") shows Reach's aftermath.
Multiple human spacecraft escaped before the Covenant glassed the planet, saving John-117, Riz-028, Soren, and Doctor Catherine Halsey.
John-117 discovering the first ring is Halsey's priority over avenging ONI and UNSC High Command.Kai-125's fate is revealed on Onyx, the secret UNSC world, with ONI's Colonel James Ackerson.
She appears to be Ackerson's right-hand woman after teaching his Spartan-III troops. Reach's aftermath differs greatly from the games and novels' primary narrative.
Games and literature diverge greatly after The Fall of Reach. John-117 and the UNSC ship Pillar of Autumn use Cortana coordinates to leap from Reach's death to the first Halo ring after examining a Forerunner relic.