Plan F is not going away if you are on it before 2020. Plan G is similar, except it does not cover the Medicare Part B deductible ($183 in 2017).
The unknown factor of course is if the premium for F will remain affordable -- who knows.
There is little point in trying to plan way ahead regarding Medicare, as the rules and fees change every year.
A reasonable approach for a new Medicare person would be to choose a G plan. The Blue plans are recognized almost everywhere, and that is what I would advise as the least hassle-y solution.