That was the clincher for me. You've given more than generous notice, you know it's his responsibility to find your replacement not yours, you're looking forward to closing that door for the final time at the end of October. Stick with that. When you have more availability, as you also note, new doors will open, even more clients possibly, but you can pick and choose the ones you actually like to work for. A weight will lift when you walk away. Also, I do hope you are being appropriately paid for the extra time needed to train up the untrainable person, it sounds quite a frustrating task.