I don't think it necessary to advise the therapist ahead of time nor does there need to be an additional closure appointment regardless of what the therapist wants. I can see telling the therapist at the beginning if you want to tell the therapist why or if you do not have anything else to discuss with them.
I left one, who was horrible, who told me I could not just quit without us discussing it and I was like no - I'm just not coming back. And I left - no more discussion. I did not feel bad about it = it was a relief for me, and I did not regret not discussing it with her. But that is me.
It is true that some therapists may like to have a separate closing appointment, but their desire to do so does not create an obligation in the client to comply or gratify their preference.