Here's my (completely) wild ass guess for the series finale: Walt thinks he can walk away, but he can't... he's in too deep. Plus, he knows too many people and (now) too many people know him. Even with the massive hint that he now has, I think Hank will become something of an unwilling ally to Walt. Guilt, family loyalty, grudging admiration for the best player in the game... all that stuff will influence him to just keep it under his hat. But I don't think he'll actually take Walt down. I think the M60 is for the skinhead gang that Todd is going to set loose on Walt once Lydia enlists Todd as her new go-to guy for the needed international meth supply. I think Walt and Jesse will defeat the skinheads, Todd and Lydia in their last great act of defiance. But I think Walt will die in the end. And I think it will be Jesse that kills him. The way I see it, the only person who can kill Walt, the only person who I can see it coming from, would be Jesse. Only Jesse finds some spiritual redemption, takes his money, says a last goodbye to Saul, hooks back up with Brock's mom and rides off into the sunset.
And just because I've never liked her from the first episode, I hope Jesse shoots at Walt twice and the first bullet catches Skyler right between the eyes. Hank and Marie can raise the kids. Even better, maybe Walt, Jr./Flynn will cap her. He can't stand her anymore than I can.
The end.