A Rafa-Novak final would be grand. Unlike 2015, Rafa is in good enough form that a Novak victory would be well-earned, and Novak is in good enough form that Rafa would actually be challenged by him. It would also be the most important slam for Novak to win to pass Rafa, as not only would he be adding to his tally, but he would be taking away a win from Rafa.
That said, I think it is a foregone conclusion that Rafa passes Roger, and Novak passes Rafa. It is the way of things: records are broken. I just think that Rafa really wants to pass Roger and will do what it takes to stay fit enough to do so, and likewise with Novak. So we'll probably end with:
Novak 22
Rafa 21
Roger 20
I do not think that there is a foregone conclusion in sports especially with the Big Three in tennis. Also, while records are meant to be broken it does not really equate that it will happen.
Yes, there is some biased in my post because I am a Nadal fan but at the same time that I watched enough sports that anything can happen. I still remembered telling myself in 2010 after Nadal completed the Career Slam that it will be very hard for him to surpass Federer. The reason I told myself like that because I believed that Federer was great he will win enough slams to fend off Nadal. This is before Djokovic 2.0 came...
Then, fast-forward into 2020, I am still surprised that Nadal is only 1 behind Federer with a great chance of surpassing him either this year or 2021.
That's the same thought I am holding about Djokovic. He is an all-time great and I believe he can potentially become GOAT (even surpassing Nadal) due to his records and play, but for him to win 5 more slams after the age of 33 is a very daunting task. I would not be surprised one bit if he does it, but it will really take a lot of him to accomplish that feat.
When Federer won the 2018 AO and reached 20 slams, I told myself that man Nadal has to 5 win more slams and hopefully Federer does not win another slam just to surpass him. While Nadal has won 3 slams since then and unluckily Federer did not converted two championship points (20 > 19), and Nadal still has to win 2 "more" slams to even surpass Federer. Djokovic is in the same boat as Nadal two years ago but the difference is that Nadal has a better chance to win a couple more slams. So, Djokovic might really have to win 4 to 6 "more" slams just to surpass both Federer and Nadal. That's just insane to think about!
As for Nadal, while I do think he is thinking about Federer's record, I think deep down he really just wants to be competitive and play at a high level. 21 is not a set number. It is just a number for him. If he reaches 21 slams, he won't think like, "Okay, I got 21 slams now I can retire happily..." He will try his best to try be competitive and win more slams.