Heck, since there is at least minimal interest I will expand on what I mentioned here. Feel free to PM me if you want to discuss further. Almost all feds retain their health insurance in retirement because it is a solid reliable program. But you continue to pay the full freight after Medicare kicks in even though the Fed program no longer handles the primary hospitalization costs at that point. The primary choice you have to make is whether to pay ~$100/month more for Part B. if you do, the Fed insurers promise you won't pay any out of pocket for anything (assuming you stay in network and with Mediacre accepting doctors). The calculation to make is whether it is worth $1200/ year each to avoid deductibles and copays. Many who do the analysis conclude that it isn't. My decision not to take Part B was based on current costs and my conclusion that the max out of pocket we could face in the future is not very daunting in any event. If I conclude that I would have saved a few bucks with Part B, NBD. The downside is that Part B goes up 10%/ year for every year you delay signing up.
The other issue - whether to sign up for Medicare at all is more confusing. Technically, your FEHB policy remains in full effect so Medicare seems superfluous. But, the policies all state that they will only pay Medicare rates for Medicare eligible policy holders. So doctors visits are paid at the Medicare Part B rate rather than the plan rate in any event. If the plan continued to cover hospitalization, that would only pay Medicare A rates as well. The Government and all the plans push Feds to sign up for Medicare A and I have read of confusion and slow payment issues plaguing some who chose not to so I wasn't interested in testing those waters. I have read some questions about whether it would be better to skip Medicare A if retiring overseas but I haven't read enough to know whether that makes sense.
I don't know why the law was never amended to require eligible Feds to sign up for Part A. I guess when they started deducting Medicare coverage from our salaries and made us part of the program they forgot to add a requirement. It hasn't turned out to be much of an issue since most assume it is a requirement and sign up (like I did) even if they find out that it isn't.