1. Federer, having discovered new form, would be a 9-time Defending Champion at the AO, and going for his 6th straight Calendar Year Slam.
2. Nadal, having undergone a wondrous knee-operation, would be wondering if he wants to stick to Golf or Football (having tired of Tennis). He'll decide on Golf seeing that he can't get Spain to the Finals and the Cup by himself and he's tired of other stars from Real Madrid stealing his spotlight. He'll go on to become a 500-time Grand Slam champion in Golf, living till the ripe age of 258.
3. Donald Young loses to his 4 year-old son 6-0, 6-0, 6-0 in an exhibition match at Wimbledon
4. Djokovic gets a heart-attack after a particularly hard chest-pump which puts him out of Tennis (don't ask me how).
5. Murray decides Olympics are more prestigous than Grand Slams and wins his second Gold Medal at Rio, and eating Doritos on his couch waiting for the next one to come about.
PS - All trolls