The 2 most likely end game options, IMO.
1. Breaking Bad is a tragedy. Like in Scarface, Macbeth, etc., we have seen the primary protagonist's ascension into power/control/wealth. Walt is now becoming incredibly ambitious, and perhaps more dangerous, cocky. Probably somewhere close to the middle of the 5th and final chapter, we will see Walter White peak, assuming the role of drug kingpin. He will then crack, and spiral to his demise until the end of the show, eventually dying or being arrested. More likely, his cancer will come back, and kill him. There was one particular scene that was thrown into the 4th season in which he was at the doctor's getting tests done to see if he was still in remission. Later in the same episode, over dinner, Walt Jr. asked what the results were. After a slight hesitation, Walt said he was still in remission. Maybe I'm reading too far into that, but it seemed as if he was withholding some information. Either way, I would not be surprised if the cancer came back and killed Walt just before the end of the show.
2. Jesse somehow dies, and Walt realizes the severity of the circumstances, and retires to live happily ever after.