this is sort of a contradictory sentence seeing as GRRM hasn't had any control/overseeing to the show since season 5.
I'm of the belief that both the books and shows are heading to the same destination, just on different paths. The show has to take some shortcuts here and there, but I think George will ultimately decide what happens to the most important characters on the show.
I think Jon just has way more going for him story wise. He's a main character. He has been since episode one. Stannis isn't paraded on HBO ads, so I can't help but think that Jon is so much more important to the story than Stannis. Jon is a Stark. Some could argue that the Starks are the main characters in the story and who we should be rooting for.
Too much, in the books and in HBO's promotion of the show since the first season points to Jon being one of the two main characters in the show (the other IMO being Dany).
Which brings me to this point:
He doesn't want the iron throne so him coming back to unite with Dany is just as farfetched and not part of the book story (show story who even freaking knows anymore)
I hate this theory so much, man. It's so damn fairy tale and I would hold that against GRRM until the day I die if he does something like that.
But I think Jon just has much more to do. He's deeply tied to so many different storylines. The Lannisters, The Wall, The Red Witch, The Boltons, Winterfell, The Night's King.
Too much has happened, and we've seen too much hero questing from Jon for him to just die and to be done with it. If he doesn't come back, what was the point of going against the books and actually sending Jon to Hardhome and give him a moment with the Night's King. You could say it was a hint of what's to come, but why Jon?
I cant shake the feeling that Jon still has some unfinished business with the White Walkers and all of the other storylines he died in the middle of.