I will allow a class to run if attendance pays the instructor and I have no other class to fill the spot that can do better. Classes with low enrollment get moved to less favorable times. Many classes have run for quite a while like that and then suddenly had great numbers.
I haven’t had a problem with late instructors, but I have moved classes to times that worked better for the instructor if it works for them and the studio. I would replace an instructor that was always late. Once every 3 months would slide, but more than that and I would have a problem. If an instructor was late once every week or two, I would teach the class myself if I had to until I found a replacement.