I'm thinking about feeling abandoned rather than being abandoned here.
I felt abandoned in a sense by T1 when he moved the boundary goalposts. In reality he didn't literally abandon me. (I felt similarly about my mother actually.)
In terms of what you mentioned about a particular client filling a therapist's needs, I think I may have done this for T1, and his unsolicited contact recently makes me wonder if he felt abandoned by me when I left him. Again, I am talking about feelings of abandonment, not actual abandonment. I didn't abandon him because I have no obligation to him at all.
So in the sense of feeling abandoned, probably yes both ways. In terms of actual abandonment, no.