(1) If a member posts a message requiring approval, but then leaves the group (perhaps by their own doing, but definitely if removed by a Moderator) before the message was approved, the pending message remains in the queue, still waiting to be approved.
I wonder what would happen if that message is approved. (I did not try.)
I just had this happen a few days ago when a member posted a moderated message, then left. After I approved the message, it was posted to the group as normal. The entry in the log says "approved 's message #1803". I can click on the message title that follows to go to it and see who posted it if I have a need.