Basically the answer is never cancel your retreat. The big mindset shift retreat leaders need to make is that they are building a lifelong business. Each retreat you do builds your future. When running the retreat you increase positive customers. You gather pictures. You gather video. You create testimonials. All the things you need for your future. If you cancel your retreat you miss out on all of these things. 

Most people think their retreat is a weekend or a week long  experience. But from the leaders perspective it should be thought of as a year long process of building positive momentum. If you cancel you halt all that momentum. Lastly its ok to lose money at first. Just as every other business doesn't expect to make money in the first year, give yourself some time to build your business which will serve you over your lifetime.