If Froch wants to have a greater legacy than Joe then he needs to avenge his defeat Ward. I think Froch will not risk doing that whilst he is on a high and wants to cash out in 3/4 fights.

To have a good legacy other than Ward would be beat Junior, Kessler (rubber match), GGG and possible unification AA/Degale/Groves (you never know Groves may get back by then).

Froch could go up to light heavy and take on Hopkins/Pascal/Kovolev/Stevenson as a final fight.