Considering the timeline, I think the options are probably:
1. Whether he starts a war with the red court over Susan, or
2. Whether he runs away with Susan to South America
Personally, I think that 2 makes the most sense because he really does consider it, it is a decision we can really see Harry choosing. The problem is, it makes for a terrible story. He’s gone from Chicago and isn’t there to stop the Fairy court war, to stop Nicodemus from kicking off a huge plague, or to stop Cowl from becoming a God. Those things ravage the world and make it a hellscape and Harry learns he should never have left Chicago? That seems like a poor lesson.
So I think it is choice number 1, he refuses to save Susan because a war would be too deadly. Because of that he loses his moral center and increases in self loathing which allows him to become a bad guy. He probably accepts an offer from Marcone, but eventually turns on him, then accepts a denarian coin, but discovers they don’t play so nice with each other either. Maybe accepts the winter night mantle somewhere in there as well, but isn’t as good at managing it as our Harry. War kicks off where Red Court goes after the council allied with outsiders and the Fomor, who go after the fairie courts. Massive war going on with no good allies and he has taken to summoning other version of himself when danger looms so that they can be killed and he can escape with people thinking he is dead. At the end of the book Harry has to face off against himself and “save him” to be able to get home. Possibly by either making him the winter knight or bringing him into line as winter knight so he can get Mab’s help in getting home.
I don’t see it being a choice about the sword, because that happened earlier than “the end” of the book.
This could all be wrong, it would be a very different book if the Harrys trade places like the Kirks do in Star Trek, but it wasn’t my impression that was how it was going to be written.