Terminator Genisys Ending: What Does It Really Mean?

How Can John Exist If He Isn't Born?

At the end of The Terminator, Sarah muses on the paradox central to the series - if John doesn't send Kyle back, then he can't be born. This has been a constant throughout the series, providing the main motivation for Terminator Salvation and a key plot beat in Genisys. However, this status quo is totally destroyed by the end of the film. Even though Sarah and Kyle have fallen in love, it's very clear that a version of John doesn't exist in the new timeline. But there is still the original John, now a Terminator, running around. To make sense of that, we once again need to look at Genisys' bizarre time travel logic. If each timeline is an alternate universe, then a new one is created when someone travels back and alters something. The specifics of this are glossed over (mainly because, as a fictitious construct, it doesn't actually make any logical sense), but essentially the events of previous alternate timelines still exist alongside the new adventures; it's just that, as we can only view/access one timeline at once, they appear to be overwritten. That's how the Terminators, John and Kyle can exist without any in-universe origins - they've just jumped realities. As for John parentage, the Kyle who fathered him is from a different timeline to the one we spend most of the film with due to the divergence.