I, like you, am a partner in a small firm. My treatment was RT so I needed plenty of time off for appointments, but not a very aggressive treatment. It was easy for us to schedule work so I had nothing important (well not urgent) to do. So I think just try and arrange light duties for 12 weeks post op. You may find you can do everything and take on more, but as long as you can make sure you could drop nearly everything and it won't crash the business you will be fine.
Good luck with the insurance. Mush as they like weaseling out of paying, I can't sees anything they could argue about.