Novak Reset
He might want to emulate the Fed. This could include an equipment upgrade, a change in playing schedule to focus on important events and fewer overall matches, and a review of his physical training and dietary approach. All those needs change as we age. As a final consideration he might want to look at changing anything that might fall into the category of a weakness. Looking at his game it is hard to find any. If I had to choose I'd suggest he work on his net game and maybe even play doubles to raise his level in that area. He has few if any visible weaknesses.
Final Analysis: All this goes back to focus. He is now married with a child. I never remember a Pro that didn't drop his level of play when family became an issue, at least for a time until some balance was achieved. If personal issues come along this can destroy focus.
Married
Falling out of love with tennis?