Realistically, he only has a good chance at Wimbledon. My guess is, Federer has 1 more Wimbledon title in him before he retires, but 0 wouldn't surprise me either. I'd be amazed if he wins more than 1 slam until the end of his career.
Well, I will not be amazed if he wins 3 or 4 more slams. I agree that Wimbledon is his best chance, but he can definitely win US Open as well. Remember those semis against Novak in 2010 and 2011? He should have won at least the 2011 semi and faced Rafa in the final. Not that he for certain would have beaten Rafa, but I think he would have had a good chance. Last year was a letdown, but that walkover against Fish was not the best before meeting a brilliant Berdych in the quarters.
Even in Paris Roger was extremely close in 2011. For some reason he played an awful RG last year, despite having a cakewalk draw to the quarters. It was perhaps his worst tournament next to Miami.
Of course it will always be a tough ask to beat Murray/Djokovic back-to-back, but he overcame the challenge in Wimbledon last year. And it is likely that Murray or Djokovic will have a bad GS now and then.