I dont know how the show runners would do it. The way they have been doing things lately I thought of the dumbest way they could do it and thought the Dumpster scene from TWD lol. My initial thought was it being tied to Bran somehow. That thought has gone out the window tho. The actor who plays the NK has been tweeting about how babies and dragons reacted when he touched them and what do we think will happen since he touched Bran. With all the NDA they sign I doubt he would talk spoilers only troll.
I just hope that either he returns via warging into Bran or Arya or One of Krasters Babies being left as a Heir or anything really. Or they do some explanation. There are way to many plot holes ending it the way they did.
The way I see it is the show runners had Bran go north for the sole purpose of having this battle that led to nothing. Had Bran stayed south, The NK could never kill the Raven, never mark bran and thus never be able to break the wall and go south due to the magic on the wall.
Bran went north to basically become the 3eyed raven tho? not for the battle to be had in winterfell. the only Kraster baby left is Sam Jr who was never given to the night king. and how can something dead Warg into someone? the directors tried to make something that is nothing in the books into something which was IMO a huge mistake and had lead to many being upset of how he died.
That is whats puzzling. Bran had this important role to play but if it ends the way it did he only served to allow the dead thru the wall. There has to be more than Cersie. It has to be about killing him for good as it is the only way to get rid of him forever. Mel mentioned Azul Ahai grabbing the sword from fire called light bringer and the sword is the only way to truly kill the long night. Last season she mentioned bringing ice and fire together and mentioned the price that was promised to Dany. and all the sudden she just disappeared.
Dany had the vision of not reaching the throne and then seeing her child and Drogo. So in some way Dany should die prior to getting to the throne as seen in the vision of her in the afterlife. Jon being the prince that was promised will have to be the one to kill her to truly create light bringer. Maybe the rest of the red prists show up and inform him lol.
As for the warging part, Its been documented that people have warged seconds before they die. In the books some speculate Jon warged into Ghost when he died. In the show the wildling warged into the eagle after Jon killed him.
That led me to the idea that the NK warged into another body and would eventually lead to him transferring into Bran but the actor trolling makes it unlikly. He did tough Arya and could posses her and she would become NK. That would make her a kick ass assassin of the god of death and Jon having to kill her with light bringer would fit the bitter sweat ending GRRM said it would have.