Nadal's draw through the semis was no cakewalk. Excellent players. But he got through w loss of one set. Medvedev proved to be a tough opponent - a fifth seed who appears to have the mental strength of a champion. Legit Slam title for Nadal, beyond question.
Other side of coin - don't assume even the short-term future. Don't think Medvedev is going fall off, think he is here to stay. It also looked like he had figured out a way to play Nadal during the course of the match. Thiem is very, very close, and I think very likely to finally take the Musketeer's Cup off of Rafa's hands. Tsitsipas simply played way too many matches the first half of the season for his young body. He will revive and is a danger to anyone. Zverev will also come back. At some point he will stop pouting and go about being a tennis player. As soon as he does that, I think we will start seeing him fulfill his potential. Presumably, del Potro returns and is healthy. The young guys mentioned are also going to be a year more mature and physically stronger.
So, for 2020 I think you have a more open-ended situation than in past years. Really this hypothetical (but likely) top eight could all be very close: Nole, Rafa, Mdv, Zverev, Thiem, Federer, Delpo, Tsitsipas. Then there are some interesting wild cards who could beat Nadal or Djokovic on any given day, including at a Slam: Auger Aliassime, Khachanov, possibly Rublev or Shapovalov, and, of course, Kyrgios.
Another scenario is that Djokovic is motivated to put it into yet a higher gear, and cleans up next year. I personally don't think this is will happen, given the competition, and given the mileage on Novak.
Splendid work by Rafa; Slam earned. I tend to think it may also be his last.