It is so simple it is ridiculous.
George R.R. Martin is setting up his female characters to lead in the end.
Every strong male lead filling a traditional leadership role will end up dead or neutered.
With this in mind expect the final battle/story line to coalesce around Danaerys, Margery, Arya, Sansa, Cersei, the Sand Snakes, Brienne of Tarth, Yara Greyjoy and Melisandre.
Expect any remaining traditionally strong male leads to be killed or neutered (along the lines of Theon).
With this in mind do not get close to the following:
- Jaime Lannister
- Roose Bolton (who would though?)
- Petyr Baelish