So here is my theory for the ending:
It involves the three heads of the dragon prophecy.
We have always assumed that there would be three riders working together, so . . . Dany, Jon, and Tyrion. However, I believe this is foreshadowing another conflict. I believe that Dany is becoming cruel and unmanageable. While she still claims to serve the common people, in reality, her conversations center around the Iron Throne. Jon will notice this. I believe that Jon and Dany will first become first allies (against the WW), but ultimately, Dany's successes will cause her to overstep boundaries.
Jon will be the second rider and will OPPOSE Dany, not be aligned with her. He wants to protect the North and they want to be free of the Seven Kingdoms.
The third rider will be a White Walker. I believe the Night King was originally a Stark and, as such, has the power to warg. Thusly, one of the dragons will be fighting for the White Walkers and prove to even out the playing field so to speak.
Cersei will simply sit back and let these three battle it out as it works to her advantage to have them all kill each other off. All she has to do is SURVIVE and when these three are battling, it is easy.
There will be nobody ultimately on the Iron Throne as the region will be devastated. However, the White Walkers will be defeated in the end and each of the regions will have so few men that they are not ABLE to attack each other. Thus, they must grow food and become peaceful societies far away from each other. This is how mankind "begins" and eventually morphs into what we know today. All of the former glory and power of the Seven Kingdoms is stripped away leaving only farmers left to rebuild.
The entire series is a warning that we are entering into the same kind of paradigm where the common man is no longer valued and only serves to serve the rulers. Farmers and tradespeople are killed mercilessly, while they are the actual keys to peaceful and productive societies. Thus, when we place power in the hands of the oligarchy, eventually everyone suffers. The few who can avoid war (Pot Pie "I am a survivor") will be left behind to pick up the pieces.
(And the Hound will be a wonderful farmer with a warm family who loves him. He will name his first born daughter after the young girl who starved to death)