Original Medicare, Medicare Advantage, and Medicare Supplement plans are NOT able to drop you based on your health status.
Original Medicare, Medicare Advantage, Medicare Part D, and Medicare Supplement plans are guaranteed renewable as long as you continue to pay the monthly premiums.
Keep in mind if you want to change plans, there may be restrictions or roadblocks due to health. Medicare Supplement plans can deny your application based on pre-existing conditions except when you are first eligible for Medicare Part B.
Medicare Part D and Medicare Advantage plans do not review your health history. However, you can only apply during certain times of the year.