I have been to a number of closing performances, and I am not aware of any particular rituals that apply to all shows. The quality of the show itself may well depend on a number of factors including the size of the cast, the content of the show itself, and how long it has been running. Many times the final number includes tears as the cast members say goodbye to part of their collective life. Some shows have curtain speeches, some do not. I am confident that SITPWG will be a lovely poignant final.