I actually would agree with Fedor considering retirement at this point. He has nothing left to prove.
Sure, he could always find that fire again and start winning for a bit, but let's be realistic, 90% of all fighters, and athletes in general, are NOT fine wines. Modern day fighters who manage to keep competing at the highest level after the age of 40 are few and far between. Hendo is a warrior and legend of MMA, just like Fedor. In fact, it could easily be argued that Hendo has a better resume than Fedor.
Regardless, is the risk of sliding further down the mountain worth it to Fedor at this point? I'd say no. Obviously he never wanted to get in bed with Zuffa, and he probably feels like the buyout of Strikeforce put him in a tough situation. Walking away now still leaves him with a very strong legacy intact and it would be inline with his humble reputation that has been built up over the years.
That doesn't mean I think it would be out of line for him to fight again. I just think he's come to a crossroads in his career where he has to make a decision on where he wants to go. If he continues to fight, it may mean he is reduced fighting much lower level competition, which is a criticism that has already plagued his resume by many critics.