I guess Season 8 is 8-10 weeks away?
I think there's a good chance Jon Snow won't survive, if at least the series is true to GRRM's tone. I mean, it would be a "happy" ending maybe if he did, but the thing is that he is on borrowed time. He's already died. He's back mainly to serve a purpose. Once that purpose is served, his role would be finished. Maybe there's stuff I am missing from the book or lines I've forgotten that might suggest otherwise, but comes down to Martin's sensibilities and what the showrunners decide to do; and Jon seems to be burdened by that sense of nothingness he experienced while dead, and came back to play a part. Martin was really harsh on Tolkien's Gandalf for his supposedly "easy" resurrection
[personally, I think that's unfair -- Gandalf wasn't a man, he was basically an incarnate angel and sent as an extension of the Illuvatarian Gods from the west, so if they want to send him back in a more purified form after centuries of living as a man had diluted him, that's their prerogative... he didn't really exist as a human character when sent back, he was an emissary... so he and Jon are in a different league, perhaps, since Jon was always mortal, even if he's also been sent back to fulfill a job]
and if you note all the people who are alive after death in Martin's series (except maybe Beric?) are in a world of hurt and/or a form of bastardization of life. Lady Stoneheart. Robert Strong. etc.
I dunno. As far as who will take the Throne, if they follow GRRM's approach:
1. There won't be a throne and it'll be dismantled and/or some kind of new arrangement. Out with the old. In with the new. This could even involve some sense of balance with the Wights but I'm not sure because while there is a backstory there we don't know yet, they keep being portrayed as destructive and evil at least in the show... anti-life, a bastardization of life.
2. It'll be someone unexpected. Again, the old system passes away. Something new arises.
My biggest fear is that they will ruin this show by continuing to resort to the sentimental and the expected. The best part of the first few seasons is that it consistently deviated from expectation.