I have a theory that Melissandra sacrificed Stanis and his army for John Snow. She went straight to the wall. She also talked to John and said I see greatness in you and that there is only one true war. War between the living and the dead. I don't see how they can let him die. Just a theory.
Kit Harrington said he is done with Game of Thrones. Maybe he is faking us all out, and your theory is solid if they were to bring him back, although apparently the showrunners let drop that they are not big fans of bringing major characters back from dead, which is why there was a notable absence at the end of this season relative to the books. It could also be that Melissandre just wanted his royal blood.
I think the flags will burn because of Sansa. The north is still loyal to her and I think she gets the banners together to take back Winterfell!
Solid theory.
It was a quick end for Stannis, which is why I was a little pissed off last night. I expected him to take Winterfell and for Ramsay Snow to meet a grizzly demise, and Stannis was the closest thing we had to a central character this season. That was a whole lot of screen time to just suddenly end as if it never happened. I did like Brienne taking him out, although it was a little far-fetched that she would find him in the woods at the end of the battle, with no one noticing the 6'2 chick in clean armor.
Renly was the first death that really frosted me because it was with magic and I really don't like plot twists that involve magic killing people, because if that is possible, why doesn't the side with magic just cast a spell to win? Renly was also the one I was rooting for to win the War of the Five Kings. He was by far the coolest of the choices.
I am glad that Sansa escaped, although the absence of the Vale and Littlefinger after about the 2nd episode was a little strange.
The producers salvaged about an hour of silly screen time from Dorne this season by killing Mycella. That was the first interesting turn in the entire Dorne arc.