Who did Calzaghe actually beat? He should have never left the game how he did - there were at least three more fights out there for him to take and arguably win.
I doubt Joe would be so stupid to even attempt a comeback after such a long time away. He's now advancing in years, and has been spending his time dancing very badly, pulling Russian mail order brides, and snorting white powder that is probably 2% max in any way related to coca leaves. All he would be doing, would be risking his legacy, which although there are holes in it, as is the case with most fighters, is pretty decent.