Calzaghe can fight Taylor, Tarver, Dawson, Pavlik, and re-match Hopkins. Retire at 50 wins undefeated.
While that would be awesome to see.... and Calzaghe is still fighting at a very, very high level, he is 36 years old and all 5 of those guys are solid fighters. It would probably take close to 2 years or more to pull it off but if he did you could probably put him right up there, and possibly ahead of a prime Roy Jones Jr. as the greatest super middleweight/ light heavy of all time without any debate.
I don't know how the Pavlik fight would work for because it is obvious that Pavlik fights better at middleweight, and Joe will most likely stay around 175lbs at this stage in his career. He would embarass Pavlik at light-heavy.
I don't think I would be too terribly interested in the Hopkins fight either just because I don't really find Hopkins overly entertaining to watch when he is matched up with such an active fighter like Joe, he clinches way too much, and as seen in the last fight, just acts like a little bitch at times with the low blow fakes and whining about the behind the head punches. No way in hell would I put any kind of money down to watch it.
Joe would own Taylors mind before the first round was over.
I would have to say out of the five I would want to see Dawson the most then followed by Tarver, but I just couldn't see Joe fighting Pavlik unless Kelly just went on a two or three fight tear destroying his opponents and Joe would be willing to drop down to a catch weight of 165 or so.