I dont think so. I depends how much they love competing I guess.
Ive never really heard Crocop in interviews. So I dont know how much he really enjoys fighting. Retire because of 2 losses, I dont think so.
I really think Liddell just likes fighting people. I think he's happy with his success, but Im sure he would fight dudes for a couple of bucks and an excuse. I dont think he'd be happy waking up, knowing he cant punch someone in the face legally anymore. So, No, Liddell should keep fighting until that hunger to punch people is gone.
Hughes I dont know neither. He's accomplished alot and if he feels he can lead a full life after fighting, he shoud. Because, if he can be just as happy preaching the word of god as he can be smashing someones face, might as well do the more passive option and leave his legacy intact.
thats what I think.
As for retiring because of 2 losses, or because there is tougher competition out there etc. That should not be the reason. People should retire when they dont like fighting anymore, not because the public thinks they are no longer contender/championship material.