Yes that is possible to do but just like our core selves, we have fears that prevent those aspects of ourselves from returning. It doesn't know the state in which our core selves are in, it just assumes that it is in a better place (which is why it went there in the first place). But it would be possible without the use of a shaman to retrieve them, but would require a lot of psychotherapy probably and preparation to ensure that it will be welcomed upon return. However, this method could take years for your lost parts to be able to return.

I think about it like if we were lost on earth somewhere and had no idea how to get back or even if we wanted to come back. The only way we might find our way home sometimes comes when we are called. If our lost selves receives the signal we have sent out then it is possible it may be heard and pursued, but not likely.