Been thinking about the next season, and here's what may happen. I'll forego the spoiler tags because if someone is reading this and hasn't figured it out from all the previous spoilers, they kinda deserve to be spoilered.
Gus and Don Eladio and his cartel dead, and that creates a massive vacuum and dries up the supply of crystal meth in the American Southwest. Somebody will step in to fill that void.
The fire department will put out the fire in the lab, which will of course uncover it and vindicate Hank. The laundry, Pollos Hermanos, and all of Gus's business will come under scrutiny. Surviving managers of these businesses (especially the laundry) will be investigated. This will happen, though I'm not sure I can see it making a good story.
Walt now owns a car wash, a paid off condo and house (I think he paid those off; I could be wrong) but after Skylar paid off Ted's IRS bill, and Walt bribed Saul's secretary, the man is broke. He's also still got lung cancer, presumably, which is not fully cured but rather still in remission. I'm thinking that Walt is going to go back to cooking crystal meth to support his family and pay his medical bills. Without worrying about Gus, Walt will have to worry about staying one step ahead of Hank instead.