The Rookie takes off his helmet, and he is a Prophet! He then flies away with the power of the gravity shoes he put on. He then gets hit by the other half of the forward unto dawn because that planet was really Earth because Chief and Cortana were sent back in time. The FUD crash lands. The Rookie (Who is still in midair because Prophets have incredible resistance to Human made Frigates) watches as Master Cheif's helmet explodes out of the FUD and bounces around the city at the speed of light. It then rebounds and hits the Rookie in the face.
The Earth explodes, which creates an inconsistency in the Halo Timeline, which destroys all of existance.
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What the title says. I dont think I could have done better.