This is an interesting question. I am aware of the walk-in cases where the original soul either exits or fades to the background; usually due to an inability to continue a life mission but, haven't considered much on other cases.
Some people who are chimeras https://tinyurl.com/ybownpgu
claim that the soul of their absorbed twin still exists and that they carry and communicate with this soul/twin. Many an artistic chimera will say that their twin's soul is their muse.
I can't say that currently I have any direct knowledge of this but I can relate to it because of my pregnancy experience and direct communication with my son's soul before conception and before/after his birth.
I was 35 when I had him, had been mostly single through out my life and really wasn't close to any mothers. My friend's children were much older than my son...and he was close to age of his cousins' children.
Anyway, during what I believe to be the 'act of conception,' I was very aware of his presence, in a sort of far away misty recognition. I had had 2 miscarriages before and feel that he was a long time trying to be born to me. But that times were not quite right for his entrance.
I distinctly remember, during sex, his presence and having the projected thought, "Okay, you can enter now." During pregnancy, I saw him many times as to what he would look like and that was correct. I was very heightened with psy abilities and shared much thought back and forth with him.
We carry a heavy karmic relationship good and not so good and he was a long time coming out. I wasn't dialating and ate 5 meals in the birthing room and went thru many tubes of induction cream....they asked if I wanted to try another tube [for a vaginal birth] and I finally told them to sharpen their knives. [for a C section] I was also afraid of normal birth due to 2 ruptured disc surgeries in my past.
So, one COULD say that I was carrying 2 souls for a time. 🤔
My intense connection continued with him after birth. Example: My sister-in-law gave a satin blanket to me at the hospital and when that silkyness touched his cheek, I was overwhelmed by feeling what he did, in the physical, but without learned words to describe the feel of that satin blanket on his face. We are still tied somewhat this way.
When I asked other mother's about this, they told me, "No, I never experienced anything like THAT!"
I have a magnet on my fridge which reads:
🍀"I smile because you're my son. I laugh because
There is NOTHING you can do about it."🍀
[got it at an Irish festival]