The theories is also one of the reasons why I love the book/show. There's so much depth and storylines intertwined that make discussing theories way more interesting than other books/shows.
Guesses for endpoints of the main characters:
Dany - Queen of the Iron Throne
Tyrion - Hand of the Queen of the Iron Throne
Jorah - Dead (seems likely he will die with grey scale)
Missandei and Grey Worm - One will die, why else do they show a love relationship building? The other stays on Dany's staff till the end... or also dies
Cersei - Dead
Jon Snow - King of the North
Bran - Not sure where and how he will end up, he will leave the cave, but I don't know how and this is hard to predict
Sansa - Back with Tyrion and Queen of Casterly Rock (I think she will realize that he was the only person who treated her right and will honor their wedding in the end)
Arya - Maybe ends up as Kingsguard or something, I dont think she remains a faceless man, but will obviously become a deadly assassin and she doesn't seem to be the type to settle down as a Lady.
Theon - Dead, probably do something else heroic for the Starks in the end that'll cost him his life
Melisandre - Dead, I just don't see her being there at the end even though she currently sits in a good position with me for saving Jon
Davos - I could see him becoming the Lord of some castle somewhere, if he makes it alive and I hope he does, he will be deserving of something nice
Littlefinger - Dead, his scheming will have to catch up to him one day
Varys - Not sure, maybe dies, but could also stay alive to the end as the Lord of Whispers for the Iron Throne again.
Jamie - I think he dies at some point, he will turn around and actually become a good guy and die in a heroic way, maybe buy actually saving the King (or Queen).
Margery - Dead, I don't see much of a point to her anymore, wouldn't be surprised if the Faith Militant kill her
Benjen - Comes back from wherever he was and is now Lord Commander, or is just dead.
I'm sure I missed some people and also these are not to be taken seriously obviously
I would have played this game as well, but your guesses are very good so now it's hard to come up with better ones.
I'll try some predictions for this season instead...
- Jon Snow will lead an army against Ramsay and will defeat him, the White Walkers have to arrive sooner or later and by the time there's no more need for a villain in the north.
- Dany will either "I am queen Dany stormborn mother of fucking dragons yadda yadda yadda" her way out of the widows' retirement home, or will be saved by Daario and Jorah, who most likely will succumb to greyscale. And of course his dragon will show up to burn shit up at some point.
- Tyrion and Varys will somehow clean up the city and present it to Dany, or either things will go so bad that she will decide "That's it, I'm going to Westeros".
- Tommen will die, a clash against the High Sparrow forces and Camp Incest will happen, can't see Cersei or Jaymie die yet. But if someone croaks, it's Cersei. If Tommen dies Margaery is no longer the queen and she may be in trouble and feel forced to confess to get out of the cell.
- Arya will be allowed back into the world as a faceless assassin. Can't see her training going on into season 7.
- The Ironborn will do whatever they were doing in the books at this point in time.
- Littlefinger must show up somehow to do some more plotting, he won't sit in the Eyrie all season long.
- Sam will learn stuff at the Citadel I guess.
- Bran will see what happens in the Tower of Joy, dunno if he will develop his skills so far that he will actually be able to contact Jon or someone else of his family.
- Sansa will reach Castle Black and probably miss Jon.
- Gendry is still rowing on that goddamn boat.
- Walder Frey is still be gloating in his empty hall. Seriously, where's some proper retribution for the Red Wedding? Roose Bolton is offed as a minor character halfway an episode and Walder wasn't seen since the Red Wedding itself.