DISCLAIMER: There will be spoilers on the Episode 3 of Season 8. I also want to be clear that I am not a Game of Thrones theorist, since I am not as entrenched in the television series as a lot of people are, so take what I say with a grain of Iron Island salt.
So far, the only Game of Thrones theorist that I have seen discussing the Night King’s death is WhyCreate felt underwhelmed by it. He states that the battle was still a good spectacle regardless. As much as a like his channel and would highly recommend people subscribe to him, that type of praise only goes so far into downgrading the overall story known for unexpected twists and incredibly high stakes for the characters. The unexpected twist in this episode for me was more confusion and less about saying “What the hell were you doing?” and more of “What the hell were you not doing?”
It isn’t so much the fact that the Night King was killed by Arya that I had a problem with. What I did have a problem with is that David Weiss and Dan Benioff missed a chance to make the death clever. Since they already take creative liberty at this point with the show, they could have had Azor Ahai show up out of nowhere, leaving all of the characters stunned with only Melisandre understanding what is really going on, Azor Ahai leads the Living Army to fight against the Night King, and after the battle is over, Azor Ahai would place his foot on the Night King’s corpse and take off his disguise revealing himself to be Arya Stark.
They could have been clever but they missed it. I am sure the fans would be pretty pissed, but they would probably be less pissed (and less confused) if it went that route. However, this might pave the way for more insight into the future episodes and the series finale, so I would expect a lot more speculation about this twist. But in my case, the directors missed the target by a long shot.
Image Attribution: Attribution 2.0 Generic (CC BY 2.0). Trip & Travel Blog “A Drone Over Winterfell!” Flickr. Uploaded on August 1, 2015. Changes include filtering. https://www.flickr.com/photos/tripandtravelblog/20201280075/in/photolist-wM7QLk