I've had a lot of doubts about DID and schizophrenia, and memories, and voices, and identities. I still don't think I get it. I know I don't get it. I consider myself functional enough for me, and when I'm not, well, I cross that bridge when I come to it and try not to disturb the troll underneath.
It's my opinion, and it's just my opinion, for what it's worth, which may be nothing, that anyone within your will remain within you no matter what. They may change in ways, you may change, or you may change how you view or interact with them, but I don't see how they could ever really be just - gone.