Here's my speculation for the finale. No spoiler tags because they're not.
Walter takes the M60 to the Neo-Nazi hideout, but he's too weak or isn't familiar enough with it and is caught before he can use it. Todd convinces Uncle Jack to let him live and work as a cook. He gets sent into Jesse's pit and after they're both too weak to physically attack one another (Walter from cancer and Jesse from beatings and poor living conditions) they start talking and come to an understanding they have to work together to escape from the compound before they can settle things between them. They don't reconcile so much, as make a truce. Walt still has the ricin and poisons the next batch of meth he's forced to make. The drug world freaks out when everyone who is using the blue meth starts dying. Walter is full-on Heisenberg and doesn't care anymore. He figures the meth world made him lose his family and if he's dying he wants to take the business down with him and destroy the Neo-Nazis' small empire. Lydia severs her working relation with Todd and he goes nuts and beats the piss out of Jesse. He actually feels betrayed and tells him Brock has to die now and then he'll die because "it's all over." While this is happening, Walter has started a chemical fire and the lab begins to burn down. Walt uses the distraction to drag Jesse out of the lab. Jesse sees their truck in the compound and the M60 is in the back. They break into it, just as Uncle Jack, Todd and the others are running out. At the same time they hear sirens in the distance. Jesse manages to get the gun working, but he's a terrible shot and only manages to get Jack. Jesse is shot and dies in the crossfire. As police cars appear, Todd disappears. Walt was shot, but lives and surrenders. At his trial he tries to absolve Skyler and Jesse by painting them both as victims he controlled. Walt is sentenced to life, but his cancer has surprisingly gone into remission again after another chemo treatment in the prison hospital so he has all the time in the world to think on his sins. In one of Walt's last scenes, Junior visits him and asks him "why?" He tells him "I did all this for you. All this is for you!" Junior replies "all what?" Walt looks at his prison surroundings and tears up. He has no response. In the final scene some time later, Todd is looking out over a pool, while he makes a call and approves a prison-hit on Walter White. He then hangs up and starts lighting matches and flicking them into the pool, inheriting the characteristics of Heisenberg.
Terrible I know, but it was the best I could make up as I went along.