In the end I guess only one of them will be left, we don't know who's the host personality yet (since I'm not sure whether Kazuha tells the truth or not). You can see it like that: every person shown until now is just one fragment of his true personality. This integration thing just means that the fragment merged with the core personality. It's just like a puzzle, put every piece of it together and you will have one whole picture. Same goes for Kazuha/Rei. His true self he was originally born with broke into many different pieces who will be slowly put together with the help of Yuuma. So you can't say the personalities disappear when integrating, they just go back to their rightful place until one whole person, the complete and true self of him remains. We'll see whether it's Kazuha or Rei. Or maybe in this case both, who knows.
There is this youtube channel called DissociaDID. Their systems host (Chloe) integrated with one of the other alters and they became Nin. As far as I remember Nin still had their memories and other stuff but she is still a different person. They have a lot of videos about DID, integrating too.You can check their channel out to learn about it more detailed
Yes I watch them but I though every person was different so it may be the same situation for each person?
Can someone please tell me what would happen if rei and kazuha would integrate because I’m still confused on the intergrate part