the only person who can be blamed for this is the producer. We have cancelled shows sometimes due to 2 or 3 people only in the audience, but it depends on the production. When we rent out the place, we continue no matter what. But, when it's one of our season's equity shows, we'd cancel, mainly because the power is in our hands, and equity does allow for these things.
other times, we do cancel because of bad weather, like this horri le storm blew in one night, and we had to cancel closing night - fire marshall's orders. But we did plan an encore performance the next week.