The physical death of the Pantheon was going to kill them. It was Norgannon's intervention that preserved their souls, from where they then began moving towards Azeroth to find new forms to inhabit. I never said that their souls did not find their way to the keepers of Azeroth, rather that they did not successfully bind to the new forms (ie: did not successfully preserve themselves).
That said, saying they did not bind themselves to the keepers is a misnomer, granted. It would be more accurate to say that the spirits of the Pantheon ceased to be themselves once they entered the keepers, as they did bind themselves to the keepers but they had no ego or will of their own (ie: the Pantheon's souls did not overtake the existing personality, and instead became sources of power for the keepers).