I just ran across this thread tonight. As regards your prescription coverage plan, the letter you received probably contained verbiage that the plan "meets the requirements of Medicare Part D" (or words to the same effect). If so, you should save the letter, as it's proof, if your private plan ever ceases to exist, that you're eligible to enroll in Part D without penalty.

BTW, I'm 71, have prescription coverage under my pension plan and have never contacted SS except to apply for my initial benefits. Everything has continued to work just fine.