Lady TT, with Rafa, I've come to believe that anything that he sets his mind to is possible, and his body somehow follows. 7 months off and winning big tournaments in 2013 within a couple of months was unreal. Usually you can figure that you double the time off before a player reaches the fitness and form where he left off.
Even if Roger doesn't lose a match at the WTF, Novak seals the deal if he can take at least 600 points at the WTF in one of the following ways.
1. 3 RR wins = 600
2. 2 RR + semi win = 800
3. 1 RR + semi win = 600
The first two scenarios are out of Roger's hands since he is in the other group and if Novak has 2 victories, he would likely be top in group A and face the second player in Group B. Of course if there is another player in Novak's group with 2 wins in RR, then he could be 1 or 2 in his group. 2nd in his group and Federer first in his means the semi would be a fight for #1.
#3 would mean that Nole is likely second in his group, and would face Roger in the semi if Roger is top from his group. This again would be a fight for #1.
It's possible that if Nole doesn't win more than 2 RR matches, and doesn't win a semi, and Roger wins the tournament undefeated, or if Nole only wins 1 RR match and Federer wins the tournament with a max of only 1 RR loss, that Roger's Davis Cup results would decide YE #1.
And of course, each RR match that Roger loses reduces Novak's requirements by 1.
So this is good news for Nole. He should have no trouble with Berdych. Stan could give Novak trouble if he is at his best, but I think he is so focused on Davis Cup, I'm not sure he'll be at or near his best. Cilic is the real question mark. He's never beaten Nole, but they had close matches their last 2 or 3 meetings and that was before Marin's US Open win. But Marin hasn't played in about a month since winning the Kremlin Cup in Russia, due to a strained right arm. Will he be at his best? So I think it's a good chance for Nole to go 3 and 0, despite having the other 2 slam winners in his group. I think 2 and 1 is the worst case But you never know, that's why they play.

Respectfully,
masterclass