Federer probably has one more in him, most likely Wimbledon, before he retires.
Nadal, provided he makes a full recovery, about 3-4 more, including 2 French and a Wimbledon. Don't think he'll be winning any HC majors.
Djokovic : 7 more over the next 5 years (2 French, 2 AO, 1 Wimbledon, and 2 US Open's).
Murray : 4 more over the next 5 years (1 Wimbledon, 1 AO, and 1 US Open. A cheeky French perhaps when he's 27-28 and at his absolute best on clay, and the cards fall in his favour).
This guys is the story of my constipation.