When Wilbur died he "split" into two separate beings. Ghostbur and Wilbur!
Wilbur- The guy who blew up L'manburg, who didn't really care about his son, the guy who snapped. All Wilbur was when he snapped minus the good.
Ghostbur- The ghost who gives out blue to people who need it, the ghost everyone love, and the ghost who can't remember anything bad. The good that was left in Wilbur before he snapped.
The reason I say this is because Wilbur said him and Ghostbur we're two separate beings and Ghostbur also said he wasn't Wilbur.
However if Wilbur is brought back, him and Ghostbur will become whole again in a sense.
