"My leaving would mean his income would double next season."
Or he may get your half from you cheap and then turn around and sell out the whole biz for next year. I would imagine he is a good person and is not set on screwing you over, BUT... he may start to get a little overwhelmed at the thought of doing ALL of the work by himself. Should an opportunity to sell for a handy profit come up he may take it. My point in this rambling....Make sure you are happy with the buyout, and then realize you are gone and what he does with it is his business.