For me, I don't think attachment or parental transference necessarily has any effect. I was very attached to my T, and had a strong paternal transference. Both were fully resolved, but healthy attachment and paternal bonds remain. I do think there were a few key points that have made it possible: I didn't come to therapy with any challenges that involved boundary issues; I never even thought about a continued relationship beyond therapy while I was in therapy (counting down the days strikes me as an indication that it's a bad idea for now); my T had (has) secure boundaries which have allowed him to both adhere to and loosen selected boundaries judiciously; he has always treated the knowledge he has about me respectfully; there has always been mutual trust; he has validated my "growing up"; and we like each other as people.

Interesting to see this thread today: he usually replies to my e-mails within a few days. My last e-mail he didn't respond to until today, about 6 weeks after. I had planned to write again today because I was a bit concerned that he either hadn't received my note, or that he wasn't well. Turns out several difficult things have happened within his family and circle of friends that took his attention and emotional energy. I'm glad he told me, which relieved my concern, and glad I could offer some support. The connection feels pretty mutual.