A good share of Medicare recipients use Excellus Blue Cross Blue Shield of Central New York. We got a letter (didn't even realize it--I thought it was the usual *if you do nothing, you'll continue on the plan*). It was in a packet that I finally opened it after hearing about it from FB friends. Now thousands of people have the same decision to make: Aetna that Cornell uses (widely accepted here, Humana no) or plain Medicare with the Medigap. I went to the Lifelong Senior Center in Ithaca to find out about workshops and there are several planned. Excellus just very suddenly decided to drop their Medicare PPO with which I've been pleased for the last 9 years. We only have a few months, for the letter came out less than 2 weeks ago.

Advantage plans are getting "modified" right now. They can
turn you down for many procedures that original Medicare
would allow.

I was told by my state retirement fund staff that it is very hard change to regular Medicare once you've been on an Advantage plan.
Perhaps others here more knowledgeable of the intricacies involved can explain more fully.