So, taken from somewhere else, someone said this that has me thinking about where the show is actually going:
The Night's King is the personification of death. Humans cannot live forever, ergo The Night's King Cannot Be Killed.
The Last Hero was a diplomat, not a warrior. He negotiated a truce.
The terms of the pact are up for renewal and the Night's King will withdraw when satisfactory terms on a new compromise are met. [finite mortal life being, metaphorically, the compromise between immortality and death].
Violence is destructive. People who fight amongst people [over the throne] are doomed [and the iron throne, metaphor for self destruction as it is, why do you think its made of swords that literally cut and draw blood from the people who sit on it? along with it]
People who reject individual ambition and prioritize the team sport of survival [i.e. Jon kneeling for the greater good] will be spared and carry humanity on. Those who prefer to win the Game Of Thrones (i.e. Cersei) will be utterly annihilated.
I think this is the the most cogent analysis I've seen of this.
I'd guess that the implication here would then be, perhaps, that Bran sacrifices himself to "negotiate" with the Night King, Jon is spared somehow in giving up any further ambition. Dany nearly is killed, until she realizes that ambition to tyranny is akin to death, and then the Night King and company go south, and kill Cersei and smash King Landing along with the Iron Throne, the "root" of the evil at hand. The Night King is satiated again, tyranny averted, they all go back to Locke's "state of nature" minus perverse "human ambition" to get in the way.
I like it, because it's the kind of simplistic philosophy this show is likely aiming for...
Furthermore, I think Bran's cryptic statement, seemingly foreshadowing one(or both of their deaths) might foreshadow instead that the paradigm, the sot of dialetic of Life:Death, Tyranny:Liberty does not end. One does not kill Death itself, it brokers an "easy peace" of sorts.
There is no "after" there is only something like the Hegelian "concrete, abstract, absolute" (that is thesis, antithesis, synthesis) of Being/Nonbeing->Becoming.
Perhaps this is exactly the point of the White Walkers, in a sense, a check on human "arrogance" and "excess." You know, just like Death itself is, no matter how powerful (or moral, or just, of kind, or whatever) you are, you still die eventually. "Thanatos" (that is, the "death drive itself, embodied) rears it's head. Except here, it's personified, as if a character.