Ever since “The Sopranos” ended on a slyly ambiguous note that kept viewers deconstructing it for weeks, shows with artistic ambition cannot come to a mere close. There has to be a finish so big it sets off a tsunami of second-guessing. Once upon a time fans didn’t want their favorite series to end; now audiences clamor for a denouement they can debate forever. People are already discussing the end of “Mad Men,” and the penultimate season concluded in June: there is an entire season to get through before the curtain falls on Don Draper and his cohorts. And that kind of anticipation sets the bar pretty high for “Breaking Bad,” the hit AMC series that has seven more episodes to go but is already awash in premature post-mortems. In this era of binge viewing, audiences feel the need to purge — the blogosphere is clogged with comments, communion and speculation. Anticipation is running so high that the show’s creators split the final 16-episode season into two parts. The first half left off last September with a kind of pre-ending: while on the toilet, the Drug Enforcement Administration agent Hank (Dean Norris) at long last realized that his meek, science teacher brother-in-law, Walt (Bryan Cranston), was the drug lord known as Heisenberg. Sunday’s episode, technically the ninth but in spirit a premiere of the second half of Season 5, picks up the story with a flash forward that echoes that of the actual premiere of Season 5 in July 2012. It’s about a year after Hank stumbled on the truth, and Walt has morphed again: he has a fake identity, his hair has grown in, his beard is bushy, he wears black-rimmed glasses and has returned to Albuquerque in a car with a New Hampshire license plate (“Live Free or Die”) and a machine gun in the trunk. It’s not clear what happened to his wife, Skyler (Anna Gunn), his children or his cancer recurrence, but his old house is boarded up and chained, the abandoned pool used by teenagers as a skateboard rink. When his old neighbor sees him in the driveway, she stares, frozen with disbelief and terror, holding a bag of groceries. “Hello, Carol,” he says. The bag slips from her hands and her groceries fall to the ground. And then the story goes back to where it left off a little more than a year ago, moments after Hank finally saw through Walt’s deception. The series never traveled too far from where it all began: chemistry. In the very first episode, in 2008, Walt was still teaching high school science and didn’t yet know about the lung cancer that would kick off his criminal career. He told his students — the few who were listening — that chemistry is the “science of change” and broke life down to its essence: “It is growth, then decay, then transformation.” In the years since, “Breaking Bad” has traced the growth of Walt’s empire, its decay and most of all his transformation. Throughout, one thing never changed: Crime didn’t pay. Killers and liars don’t suffer immediate consequences in shows like “The Sopranos” or “Deadwood” or even “Dexter,” and plenty of bad deeds go unpunished. Cable shows have license to be transgressive, and that means flouting the mores that usually guides broadcast network shows. For all its audacity, “Breaking Bad” was a throwback to a more elemental code of morality. There is a puritanical lesson to Walt’s life: he becomes a master criminal and ruthless killer with very little to show for it. Walt was able to pay medical bills, but he never experienced pleasure from his ill-gotten gains. Even in that first episode, after his cancer diagnosis and his decision to secure his family’s future by making crystal meth, he was immediately catapulted into killing enemies, with none of the fun or self-indulgence that money can buy. He became a monster, but a strapped one: Walt always seemed to need more money than he had to keep his criminal enterprise aloft. In five seasons he never took an exotic luxury vacation or even bought a new house. Finally, after Skyler shows him the stockpile of cash she hid — as big as a Buick — Walt promises her that he will get out of the drug business, and he apparently keeps his word. He is once again manning the register at the carwash where he worked, and angrily quit, in Season 1; he owns the business now, but it’s a money-laundering property that mostly owns him. His henchman Jesse (Aaron Paul) is in this last lap a sad spectacle of fear, drug abuse and remorse, at one point literally throwing bundles of cash out his car window. So the challenge for “Breaking Bad” is to end in a way that is consistent with its own consistency — viewers are in no mood to be trifled with, especially after the cliffhanger ending of the first season of “The Killing.” Network shows are designed to last as long as possible — endings are often abrupt and even unresolved. Some are just confusing: “Lost,” a highfalutin ABC series, got so tangled in its many strands that it ended in an impenetrable fog of mystification. Cable shows are written more as novels, and people expect a fitting conclusion. Tony Soprano’s fate was left hanging on the finale of that transformative HBO show. It frustrated many fans who wanted him either dead or alive, but it instead stayed true to the volatility that ruled his life as a mobster: at any minute a killer could come out of the men’s room and end it all with a bullet to the head — or not. A series that brilliantly mixed comedy and tragedy ended by straddling the two. There are many comic moments in “Breaking Bad,” but on this series malfeasance has consequences. A show that has upheld an odd kind of moral consistency could over the next seven episodes turn unpredictable. Walt took Heisenberg as his alias, a coy reference to Heisenberg’s Uncertainty Principle — and perhaps a joke on the audience.