He'll either come back as Terranort, or Terra, Master Xehanort and Eraqus. All at once. eh... messy.
Why would Eraqus come back? Isn't he dead?
After the defeat of Terranort's Heartless and Xemnas. Would Terra come back? I don't think so. If his heart and soul remain in his armor than, Terra's body would be a lifeless shell. If what I think is Terranort comes back after his Heartless and Nobodies defeat than, Terranort would come back.
Confusing as shit. >_>