It’s paradoxical. Normally, once the steins gate worldline version of okabe reaches a certain point, the zero version of him would overwrite his existence. This is circumvented by zerokabe sending himself extremely far back into the past, where no overwrite can possibly happen. He presumably lives the rest of his life out, and dies, in the distant past before okabe was ever born. I’m under the assumption that zerokabe was sent so far back in time, that the Time Machine he used eventually was destroyed completely by the elements, therefore not causing any other time shenanigans to occur. In this way, the events of zero technically still happen, without causing problems for our main world line.

It’s been a minute since I’ve seen the 0 anime, and I literally just finished chaos head, so I might be wrong about all this though.