I wouldn't worry about Djokovic's legacy. He's tied with Becker and Edberg with 6 Slams and needs one more to tie McEnroe, Wilander and Newcombe, then another to tie Rosewall, Agassi, Connors, and Lendl. I think it very unlikely that he doesn't win at least three more Slams to "pass the herd" and make it into the free range territory of 9+ Slams where only Federer, Sampras, Nadal, Borg, Emerson and Laver dwell. The question in my mind is whether he finishes with 9-10 Slams to be a step below those guys or whether he joins Nadal and Borg in the 11-15 territory.
As for this match, JMDP seems capable of beating anyone...in three sets. I just can't see him beating Djokovic or Murray in 4+ sets, so unless he puts Djoker away in this first set I don't think he can win it.