simple answer no alternate personalities with DID can not leave the body by dying, being killed off or just deciding to leave.

the more complicated answer is that sometimes integration of alters can feel like that alter is not there anymore. kind of like when someone in your family has died and they are gone. but the reality is that everything that the alter was before integration is still there, just in a different way. a more normal way like non DID people.... their memories, emotions,sense of agency is now part of either the person they reside with in or as part of another alter....

the feeling of emptiness when looking for the alter as they were can sometimes ........feel.... like that alter is gone or dead.

its actually a good thing when alters give up who and what they were as a separate alter and everything they were is joined with the one they live inside of or another alter. it shows great progress and healing. I know it does not ......feel ....... that way

I also see you have other disorders besides DID. sometime people with schizophrenia and other psychosis type of mental disorders, they can react this way too...

my suggestion is contact your treatment provider. they will be able to tell you if your alters have integrated or if you are having a symptom of your other mental disorders. if this is integration for you its a good thing. if its a symptom of your other disorders your treatment providers will help you to feel better soon, maybe even do some changes of your meds if you are on meds or prescribe one if not on meds.