Any justification for me wishing to see Royce return to the Octagon would be purely sentimental. He cannot hang in there anymore, and he could get seriously hurt.
The UFC is not, and should not, become a sport were legends from years long since gone can return for final farewell matchups. It makes the sport too much of a 'gimmick' for my liking, and less of the serious competition that it is. However, if anyone was to be deemed worthy of a final fight, i suppose it would be Royce.
A further, more obvious problem is who do you give him as an opponent? If you give him a can it diminishes it somewhat, especially if he where to lose. And if you give him a higher echelon fighter (Chael, Vitor etc) its likely he would die.
Royce has his legacy. He doesnt need to fight.