God forbid that good writing follows good writing.

You apparently have a love affair over Marcone and expect him to be a major player when he never has been a major player in the story. He's always been the mob boss in the background who Harry occasionally bumps into and interacts with.

Narratively, if you weren't too thick of it too notice, is that there won't need to be a protector of reality after Dresden takes care of the problems at the Gates. Why the fuck do you think he's a Starborn?

Harry is obviously going to kill off the Walkers and bind up their bosses in the BAT. Marcone is clearly going to get killed off at some point when he oversteps the lines Harry has set for him in his head. Marcone was and always will be an upstart mobster in a world that isn't his.

His best ending, narratively, is that Harry kills him after the BAT as there's no longer any reason for Harry to keep ignoring him. Marcone has been on borrowed time since book 1. Even he knows this as he sinks millions of dollars into protecting himself from Dresden deciding to kill him in a fit of pique.