In the Binaltech saga, the future Ravage seen in Beast Wars alters the original G1 timeline. His interference includes trapping all the Decepticons in a spacial rift, with the knowledge that Unicron would soon be attacking Cybertron. The plan was that the Autobots would have to face Unicron unaided, and the Decepticons would then be able to return and conquer whoever prevailed. As a result of these changes, the final showdown between Optimus Prime and Megatron does not occur, and Prime does not die. With Megatron trapped in the rift, Unicron does not encounter the Decepticon leader, and therefore does not make the Faustian Pact to reformat him into Galvatron.
Through the events of the story, Optimus Prime learns that the Matrix can destroy Unicron, and he and Ultra Magnus launch an assault on the giant. Within Unicron's body, Optimus Prime is severely damaged, and although not mortally, he passes the Matrix to Magnus, who completes the mission, and the pair escape as Unicron explodes.
Read more about this topic: Unicron, Fiction, Transformers: Generation 1