Let's see who gains and where.
Events that won't be held: IW, Miami, Monte Carlo, Canada, Barcelona, Wimbledon, Tokyo, Madrid, Shanghai.
Free points from those events:
Nadal: 360 + 0 + 360 + 1000 + 180 + 720 + 0 + 360 + 0= 3080
Djokovic: 45 + 90 + 180 + 0 + 0 + 2000 + 500 + 1000 + 180 = 3995
Summary: Nadal and Djokovic are closely impacted here, Djokovic lost the ability to gain many points, but there are doubts as to if he could defend Wimbledon and Madrid. Conversely, Nadal did fairly well, so he could have either lost or gained points here. In terms of absolute points that could be gained, Djokovic benefits here.
Events until the end of the year: US Open, RG, ATP Finals, Paris, Cincinnati, Rome.
Nadal defending: 2000 + 2000 + 600 + 360 + 0 + 1000 = 5960
Djokovic defending: 180 + 720 + 400 + 1000 + 360 + 600 = 3440
Summary:
Slams: Counter to my previous statement, Nadal is easily the one who gains here. Either way he was defending these points, so there was no chance to gain - now he's lost the ability to lose points too. No downside to not playing other than the ability to win another slam. Djokovic, on the other hand must play the USO if he wants to gain on Nadal in the race to #1. Severe advantage Nadal.
M1000s/1500: Djokovic can gain 2960 points, Nadal can gain 3540 points, and Nadal either can gain points without much effort in Cincinnati, whereas Djokovic cannot gain points without reaching the SF (Finals), and reaching the final everywhere else - however this also does stop him from losing points he might not have otherwise defended. Roughly equal, can be argued either way depending on how you view the situation.
Overall, this ruling is strongly advantageous for Nadal, but Djokovic can gain a good amount at the US Open. He really needs to perform well there. However, if Djokovic wins the US Open, it's practically over for #1.