- “And yet... Still you fail.”— The Didact to John-117 on his failure in attempting to prevent the activation of the Composer
Unbeknownst to him, John-117 was in hot pursuit in a Broadsword fighter, and upon arrival at the human home world, assisted the UNSC in the defense effort. Despite disabling the bulk of the ship's defenses and gaining access to the interior, before John could stop him, The Didact fired the Composer at New Phoenix, instantly killing and composing its entire population.
John managed to cause the Didact to fall into the Mantle's Approach's slipspace, at the cost of Cortana.
Though John-117 supposedly killed the Didact and the UNSC prevailed, the New Phoenix population was massacred, leaving nothing but streets filled with blue ash piles where its citizens last stood. It remained a danger zone for at least six months afterwards.
The New Phoenix event was covered up by Waypoint News Service, and an alternate cover story of a localized pandemic was instead published. In addition an ONI Agent from Section II named John Sullivan told the public that it was not a Covenant attack.
While it appeared that the Ur-Didact and Cortana were killed, neither were. The Ur-Didact survived the fall and ended up at the Composer's Forge. Cortana was actually sent to the Forerunner world of Genesis.