GRRM said that the ending will be bittersweet.
Politically, he personally is reported to be an anti-war Vietnam-era guy, and a feminist, so some expect him to leave a woman in charge, and to try to de-glamorize war, rather than have a glorious victory happy ending.
But having a lot of casualties and destruction in a big war is really more of an absence of glamorization, rather than an active de-glamorization. Despite his personal opinions, he is super story teller. People have looked to analyze his psychology, to try to anticipate where his stories might go.
I was thinking that just this morning when I brought up Jon Snow and how a lot seemed to be coming together for him but that I had a bad feeling about it; and that is that I feel like GRRM wants a female to prevail. It’s not based on anything I know about him, or his books, just a feeling I get, or a kind of gestalt undercurrent from the whole body of work to date.
The obvious female would be Daenerys, but for that very reason, might not be “bittersweet”.
On the other hand, more than just bittersweet, for a lot of people, Cercei getting the iron throne after all would be more like a bitter pill.
You have a couple of outside shots at it, but two up and coming females are the siblings Arya and Sansa. That would be bittersweet because it would entail Jon falling out of it.
There are other long shots even more difficult to predict; What claim could Gilly ever have? Or Missandei? Same with Brienne who I think is of nobility but not lineage to a house.
Also, did the red witch die?