It is very clear at this point that Djokovic is very motivated (and in good position) to try to break all of Roger's key records (Slam titles, weeks at #1 and longevity records such as most singles titles, which Roger has a good chance to own by end of 2020 or early 2021). I think Roger, unless he wins a Slam next year, should retire in 2021. There is a good group of youngsters who I think has a better shot at halting Djokovic's ambitions if Roger is not around. Think about it, it will be harder for Djokovic to get through 3 straight rounds (QF, SF, F) of, say, Thiem, Tsitsipas and Medvedev than with Fed mixed in. I hate to say it but at this stage Roger is mentally handicapped in big matches against Djokovic. It almost doesn't matter how well Fed plays, bc in the key moments he gets tight. I certainly hope Roger has a last hurrah in a Slam final where he finally takes down Djokovic, but that would be a blissful surprise rather than a realistic expectation.