I see this thing possibly playing out in several ways:
1) Jon and Dany partner up to fight the Night's King. Then Jon will stay King in the North, and Dany will be Queen in the South.
2) Jon and Dany partner up to fight the Night's King Then they fight each other; winner take all. Dany has dragons; but, Jon has Bran, who's going to get his skills up quickly.
3) Jon and Dany partner up to fight the Night's King. Then they marry and hold the Iron Throne that way. ( It's nothing for the Targaryans to marry their relatives. If a brother and two sister marriage is ok, an Aunt/Nephew marriage is super easy).
Either way, somebody is going to have to deal with the Night's King!
The Lannisters are going to be destroyed. Cersi has made way too many enemies for her house to be saved. I can see Jaime killing her. He loves her, and that's why he'll do it. He'll try to save her from herself ( Like a mercy killing. Hell, he may kill himself right after).