[sabotai]

Brandon Sanderson would be the worst possible choice to finish ASOIF (and he even said as much and that he wouldn't do it).

I'd go with Joe Abercrombie but I haven't read Kevin J. Anderson yet. Maybe James S.A. Corey but I've only read the first book of the Expanse so far.

I wouldn't be surprised if the best writer to finish the series would come from more of a historical fiction background than fantasy.

(Just looking up Kevin J. Anderson's books now and I see a bunch of Dune books and Star Wars books, so he at least has extensive experience writing in someone else's IP)

EDIT: And just looked up Corey because the "one or both halves" bit confused me. I had no idea that was a pen name for two people.