If tennis (and decline, in particular) was strictly linear,
@mrzz, then I would agree that Roger is done and Rafa
could be. But we've seen this before. I know, Roger is ancient and Rafa is old (tennis-wise). But we counted Roger out in 2013 and 2016, and now again in 2018-19. Why can't he surge again?
He didn't win anything in 2014-15 mainly because of Novak, who beat him in three Slam finals. Novak wasn't playing well when he won his three in 2017-18. So for Roger to get passed Novak in 2019, one or both of two things need to happen:
1) Novak needs to stumble again.
2) Roger needs to find his 2017 form, at least for a single tournament (e.g. 2019 AO or Wimbledon).
I think both are possible. Likely? Probably not, but possible.
As for Rafa, let's see how things look in April. We've counted him out a ton of times too. But we'll know a lot more once he starts hitting clay. I'm not counting AO out either, but I suspect he'll be too rusty to do too much damage.