While I was going to therapy, I often had imaginary conversations "with them" in my head, even just monologues about things I wanted to share with them. I actually did share a lot of those via emails to the Ts. It never became ingrained though and completely went away a couple months after quitting with each of them and I would not like to "converse" with or listen to such mental creations now. I only experienced significant and lasting internalization about people that had significant, deep and meaningful relationships with, e.g. my father or some mentors in the past. That lasts even years after the end of communication or their passing and I feel it's integrated with my own features quite a bit. The therapists never came anywhere close to that for me - luckily I should say, for one of them at least.