Not existing is the unmanifested and existing is the manifested. You can’t exist without having not existed first.
Technically, it is impossible to “not exist” once something has existed. Because if something doesn’t exist, it means it must have existed at some point for people to know it “doesn’t exist” anymore. For example, people say that dinosaurs no longer exist, but for people to be able to say that, they must exist in some way. Their physical form isn’t around anymore, but they still exist through knowledge, fossils, their cells have disintegrated and are part of the planet in some way.
Okay so dinosaurs may be a bit of a crappy example. But let’s take humans. Once they exist, even when they die, they still exist in some way or another. To not exist means to exist (Usually in a different form to what one is used to). You can’t have one without the other.
You could say to not exist means the disappearance of any physical being. But once something is conscious and has being, it can’t be taken away. It’s non-existence has been created by it’s existence, so technically it’ll always exist.
Sugar dissolves in tea but it doesn’t mean it no longer exists anymore just because you can’t see it. You can still taste its presence. It’s the same with everything on this planet. It may not exist in the form that we know, but it will always be present in some way or another.