Tricky, because GoT quite a lot of surprises.And in addition, they are not afraid to just murder popular characters in the series…
First of all, it is questionable whether the whitewalkers will win.That’s unlikely because the bad guys never actually win in American movies and series. Even in “Breaking Bad”, the evil meth-Cook went out of the pipe. His assistant was eventually put away as a slack follower and could flee live, but there will soon be a film and possibly that he will still die in that film…
Important are the Dragons.There are only two, and I believe they would survive to get offspring so that there will be dragons in the future too. Possibly one of the two is still being killed but that depends a bit on how they reproduce.
Daenerys and Jon Snow are a nice bunch and both claim to the throne.It would be logical if they managed to survive to turn Westeros back into a healthy empire.
Cersei is too evil to survive, and it would be a little bit within the line of expectations when Jaime is serving her the mercy blow to himself the pipe.Or possibly that Cersei kills Jaime before Arya Cersei is laying around. But brother and sister are going to be fierce opponents.
Arya Stark is too murderous to be ignored so I expect her to sacrifice in one of the last episodes to save another family member.She may save her sister Sansa.
Sansa and Tyrion could be an interesting bunch.They were actually already officially married and I think they are going to breathe new life in the end. Tyrion is theoretically of high nobility and Sansa too, so both can then start to manage part of Westeros under Daenerys and Jon.
Gillie and Gendrie will be able to escape and start a family and manage a library or so.
Most other main characters will end up being killed because there are not too many surviving.Missandei is definitely dead. Brienne and Jorah are brave to face their deaths. Theon Greyjoy a little less brave but he will try to save his sister Yara, but she will not survive for a long time.
Bran Stark is still a bit doubtful because his wise counsel will be necessary until the end.But Bran actually rises to a higher level, so he will be able to fight with the leader of the White Walkers by mentally taking over the undead dragon Viserion and attacking the Night King. As a result, Bran gets into a coma and then the end.
The Dragon Drogon has a major role, partly because he is named after Khal Drogo.It is at least severely injured or possibly even dead, after having taken the necessary dragon eggs together with Rhaegal. Rhaegal then continues to watch as a mother over the eggs.
Gregor Clegane is actually undead and I expect him to be possessed by the Night King and so for a surprise attack going to take care on Cersei or Jaime.His brother Sandor will stop that and succeed in it, although Sandor eventually goes down to his injuries.
In short, I expect a mass massacre…:-)