I opened my practice 3.5 years ago and never took Government insurance at all. Most people told me it would take 2 years to "build the practice" so it took about six months longer. Now I book about 2 weeks out and all my slots are full. If you "opt out" of medicare you can still see them for cash if you want too.
I would look at how many new patients you see in a month and how many are medicare and that should give you an idea of how long it will take to replace the ones you're going to lose.
