I have WP:BOLDly added a new "archive" column to the team phab board that is hidden by default. The reason for this is to give us a way to keep track of what has been finished in a given week without trying to keep ourselves and others from closing tasks when they are completed and without needing to create a new sprint tracking board each week.
There are lots of closed tasks in the done column at the moment, but I will be moving them to the archive column as fast as my "omg irc spam" feelings will let me. Once this has been done we should be able to look at what was completed each week by viewing the board with the "All tasks" filter set. I'll take responsibility for being the grunt that moves things from done to archive following the weekly meeting each week.
Bryan