Well, he has quite a bit to defend until the end of the year. Canada F. Cinci W. USO SF. Shanghai W. Basel W. WTF F. He's going to have to do well in those tournaments, hope Djokovic slips a bit in the bigger tournaments and then start doing well come Aussie Open next year. It's a tall order for him and I doubt it's his priority. He already has weeks at number one and the magic number 300+ weeks.
Champion is a RG expert, but I don't like this world #1 analysis. Fed is clearly still godly on his day, but he won't beat Djokovic's consistency over a year. It's gonna be difficult to defend the points he gained in 2014, where he had a fantastic run in the Masters events.
No matter how well someone - be it Federer, Murray, Wawrinka, Nadal - is doing, the answer to the question of them getting number 1 remains the same: it depends on Djokovic. 4 Masters titles (out of 5 so far in the year), all slam finals, and is the least prone to early upsets of all players. Until he falters it's hard to see someone else taking that spot even if they get big wins, imo. Federer down and out in 2013, Murray 2014, and Nadal so far this year, maybe 2016 will be the year we wrongly question "Is Djokovic done?" so someone else will have a chance