Jon Snow and co. have an ambitious plan for the Battle of Winterfell. He wants to kill the Night King on Game of Thrones with the hope that slaying the leader will cause the whole army to fall. It's an intriguing idea, but no one knows for sure if it will work. What happens when you kill the Night King? It's never been done before so even Bran's visions aren't going to be of much help. He can see the past and even change it, but he can't necessarily see the future. He hinted as much when Arya asked him if dragon fire can kill the Night King. "I don't know. No one's ever tried," he answered. Bran has the world's knowledge, but he seemingly can't know about things that have never happened — so he wouldn't necessarily know what happens if the Night King dies either.
That's presuming the Night King can even be killed in the first place. White Walkers can be killed by dragonglass and valyrian steel, so presumably these tools would affect the Night King too. But if you're close enough to the Night King to engage in hand-to-hand combat, you're probably already dead. Dude killed a dragon by throwing an ice spear at it, OK?
Fire kills wights, but it has no affect on the Night King, according to a Daily Beast interview with Game of Thrones "Beyond The Wall" director director Alan Taylor. "He seems to repel fire," he said of the Night King, adding, "So it's possible that dragon fire may not work on him."
But let's say that Jon Snow or Bran or the dragons get close enough to kill the Night King and they succeed. What happens then? Jon is hoping that the White Walkers and the wights, who are following the Night King's command, will drop dead without their leader. "We can't beat them in a straight fight ... The Night King made them all. They follow his command. If he falls... getting to him may be our best chance," Jon said in Season 8, Episode 2.
There is precedent to believe that killing the Night King will kill them all. In Season 7, Beric Dondarrion saw that killing one White Walker also killed all the wights that Walker had created. Perhaps the same goes for the Night King. If that holds true, though, wouldn't the Children of the Forest who created the Night King need to be killed first? They're the creator's creator. The Winterfell soldiers would be in for a nasty surprise if they killed the Night King only to still have his full army keep advancing.
There's also a theory that the Night King isn't going to show up for the Battle of Winterfell at all. He probably knows that the Starks are planning a bait and switch with Bran, and he's going to conduct other important business elsewhere. As Bustle previously reported, Reddit user qp0n10 thinks the Night King is heading to King's Landing and that his wight army is just a distraction to throw them off the scent.
The user referenced Bran's Season 4 vision of a decimated Throne Room covered in snow (or ash?) and a dragon shadow over King's Landing. Fans thought it signaled Dany's return, but, now that the Night King has a dragon, it could mean something much more sinister. And the snow could have been there to symbolize the Night King.
Either way, killing the Night King is going to be far more complicated than the Winterfell team seems prepared for. He could be resistant to dragon fire, his army could potentially stand without him, and he could just not show up at all. It's only Episode 3, after all. Killing him now would have been way too easy, so don't expect that to be the way things play out on Sunday.