Steve Danuser in interview statements indicate a possibility of planes for other cosmic forces:
Where do naaru go when they die?: “So that same rule that we established in Legion for a being of an influence goes back, if it’s killed in the mortal realm, or some other realm, it goes back to its home realm, it’s home plane if you will. That is true of demons and it’s true of other forces as well. So if Naaru are fighting in the mortal realm, for example, and a Naaru is struck down its essence would go back to the realm of Light and would be reconstituted there“.[53]
And I know that Danuzer is just being an idiot(again) and doesn't know that we saw alternate versions of the Naaru in Draenor and one of them even turned into a God Void, but maybe there's some Watsonian explanation?