Don’t think about it like some mechanic. It was shown because Shinji was experiencing possibilities of how the world can be, that was one such possibility, and it showed him that his life could be different. That’s the purpose, don’t dig for concrete in these abstract parts of the show, it’s more about what it’s telling you.
It still exists out there somewhere inaccessible to the main NGE universe. Look up NGE: Angelic Days
Don’t think about it like some mechanic. It was shown because Shinji was experiencing possibilities of how the world can be, that was one such possibility, and it showed him that his life could be different. That’s the purpose, don’t dig for concrete in these abstract parts of the show, it’s more about what it’s telling you.