I get the feeling they are dead inside. Like flesh and blood machines.
I find that is a peculiar question because without anything defined ie) their own feeling of who they are or 'soul' they themselves feel lost and perhaps without a soul. I find that with my guy he is radical when a change takes him. He literally changes his entire belief system and like a chameleon transforms. He used to be radically into religion and his language and thoughts mimicked the sentiments of the Bible down to the harsh judgements about women and sin. I find that religion and BPD are a very dangerous cocktail because it gives them the excuses and justifications for all their warped criticisms right down to feeling justified in shaming.
Now he is off the religion and conspiracy sites for his search for truth... . so now he is radical about treatment, health and normal living. I watched my guy put every fiber of his being into researching 'everything' for the acquisition of 'truth' only to discover that it is very illusive and seemingly self defeating. It made him more unstable and caused his BPD to flare and deteriorate. The more he delved into spending all his time on the net because it was a comfortable form of exile the worse I saw him becoming, more dysregulated and irrational.
It has been a journey of 3 years to try and get him to see the light with love and finally he has accepted it. He however is prone to extremes so now he doesn't want anything to do with the computer or being at home. It is these behaviors that are without any balance that makes us wonder what is inside their fragmented souls? Everything is either all bad or all good, all white or black. I have finally broken some ground with my guy into seeing that the world is rather different shades of grey with very little black or white. A break through but still he has extreme ways of dealing with things because once he deems something has hurt him then it is all bad.
I understand your question but I do believe they have souls, I just think their souls are completely fractured and barely together. I believe that somehow they were stuck at the age of their trauma and in this way are completely emotionally underdeveloped. A 3 year old still has a soul even though they are having temper tantrums but they can't develop that soul unless they mature through their many different phases. I think BPD's keep themselves from developing because they stayed stuck protecting their little child, only now they live in the adult land but they can't play fair with adult rules. Just keep them accountable and working towards their own comprehension of how things really are as opposed to their distortions. My guy wants to wield me inside his distortions to justify his warped insecurities but I have to always make an effort to NOT let him do that to me. I call him on it and then I leave it with him, that is to say that I refuse to wear what he is trying to put on me and put it back on him. I simply refuse to deal or accept what he tries to get away with in shaming, guilting and distorting me with his convoluted warped conceptions when he is in his dysregulated and unstable episodes.
What I'm saying is that I throw it all back on him and leave it with him refusing to accept any of it at all. I will tell him those words and then carry on with what I am doing as though nothing happening. I even refuse to talk or discuss any more about it saying to him and making it clear that "it is done, this conversation is over, if you want to believe that go ahead but it's garbage and I'm not giving you one more second of my time to entertain such distorted insecure paranoid notions".
Then I carry on.
It's a conundrum and one that may never have a solution, sort of like groundhog day.