We had a regular schedule and multiple games with different runners. If the scheduled runner could not make it and no other runner was available or ready to run then we played board games that many folks in the group always had available. Runners would also decide if they want to go with missing players usually getting feedback from who came as part of it. So then it came down to how much people were ok with putting it off. Granted said group would sometimes have someone buy a new boxed game and we would just play it because folks wanted to.