it would be the same scenario as Nogueira vs Schaub.
Everyone tought that Schaub would knock Nogueira out which would lead to Nogueira's retirement. 
However, Nogueira chose to knock him out and he did it! 
in fact, he could choose the easiest gameplan which is to submit him, but he wanted to send a message to all people that he's BACK! In this fight against Roy, Nogueira has all the tools to win the fight if he plays smart!!
finally, i want Nogueira to face Velasquez for revenge which i think it can happen, but it needs much time to achieve it. 
so WAR Nogueira!!! 
Both are finishers, different styles, but both are "good" on their feet, and on the ground, even if I would say Noguiera has the advantage there... Nelson can KO anybody thats for sure but I have a hard time imagining BigNog letting him get the chance. Possibly they will "cancel each other out" both having so much experience so after all I would probably lean towards Noguiera winning by decision. But my hopes are for either a KO from Nelson or a sub from Nog.