Djokovic will play to regain the number one and to defend his title. Federer? I would be surprised, i don't know about Murray but still, it's a golden chance to win a 1000 for the rest of the field, it will be exciting.
If he, in fact, does that then the Serb is really playing high stakes poker with his own season. Because he also has a final in Cincy to defend and Cincy happens to be the best practice for USO not Rogers cup. Is he going to risk skipping Cincy then?
And because if he reaches the final here in the Olympics (win or lose) and THEN plays rogers cup and cincy, his chances to defend the USO will drastically go down at some point. Does he want to defend USO or does he want to defend the #1 ranking and rogers cup? If he thinks he can do both after the Olympics.. and somehow pulls it off, more power to him. But in reality, he will probably be feeling it physically, you can bet on that, if he plays so much. Assuming your suggested scenario happens of course. He may just opt to skip rogers.