The actors are everyone who participates in a discussion, including the discussion leader.Another point of contact is the ethos of improv: the fundamental acceptance of whatever world the improv artists create while within the scene. "Yes" is always implied. (The denial of that world's reality, or "blocking," is a great obstacle to effective performance.)
There stage is twofold: 1) The room that the discussion occurs within, and 2) the text that the discussion is about. The text is a type of metaphysical meeting ground for the discussion, and as such can function as a stage.
The script is the discussion itself, which makes improv theater a better metaphor than traditional theater. In improv, the script (including the conflict and the resolution) emerge from the actors’ contributions. It’s not fixed.
However, this is also where improv and discussion part ways. Discussions require the basic acceptance and respect necessary for intellectual risk-taking, but participants aren't obligated to adopt their colleagues' hypotheses. A major purpose of the dialectic is to refine and sharpen ideas, which requires junking bad ones.
To take it further, as a teacher, it's therefore important to act out the acting--to model how to disagree without discourtesy, how to move forward without pushing others back. Improv takes practice.