The first few years featured delicious character development but most of these people, despite this or that life event, have become static over multiple season, which is a shame. Or...they become the polar opposite of what they were before, which is a bit pat.
To state the obvious, the people and their jobs are the embodiment of the 60s zeitgeist which is why the show can and should wind up. It's a hall of mirrors as we regard our past selves, America regards its unprecedented postwar economic power and standard of living, we look back at morality and all the various isms that are part of the current lingua franca of politics and, in turn, current advertising.
No doubt Don Draper will be in the last shot of the series but then Don Draper was conceived and functions as a cipher so are you really seeing a person or merely looking at an illusion similar to that which he deftly created in his professional work and personal life? The crossover into the 70s has a couple of major signposts: the moon landing (have they included that already?), Woodstock (overrated but still lazy cultural shorthand) or merely Dec 31, 1969 becoming Jan 1, 1970. The producers have mostly resisted the temptation to do a 'Forrest Gump' by involving the characters directly in historical events but those events are freely used as a backdrop.
If we go beyond 1970, in keeping with the advertising theme, the end may coincide with Jan 1, 1971, when the ban on TV commercials for cigarettes was imposed. Given the prevalence of smoking (although it continued long thereafter) and the importance of tobacco advertising to the firm and its personnel as well as the show's characters and various storylines, it seems a most obvious dénouement.
While others have changed clothes, grown more hair and sideburns and beards, Draper still has his hat, side parting, white shirt, narrow black tie and grey suit - which furthers my belief that he appears differently to every character in the show i.e. he is a projection screen for them (and us) which explains the persuasive power that begets their sense of awe when they are around him.
As for Draper being 'exposed' within the world of the show, that ship sailed several years ago. Pete found out, threatened them and they called his bluff. Don's (ex) wife already knows anyway and his clients simply won't care about his past. But the question 'Will Draper be exposed to the audience?' is a legitimate one.
And so, even a minor change in the Don Draper archetype will signal the end of an era both on and offscreen. Perhaps he quits smoking. Perhaps he quits drinking. Perhaps his hair grows over his ears or he sports facial hair. Perhaps he tosses his hat out a window, off a roof or out of the car as he speeds along. Perhaps - I hope - he finally summits Mt. Joan. Whatever the resolution, I hope that Weiner can resist some 2014-vintage socially redemptive soul butter. The dissolve to/from young man to/from old man along with the tearful contemplation of the past has been done already in 'Saving Private Ryan.' No need to plagiarize.
There's no doubt in my mind it will be ambiguous, perhaps controversial, but I do hope he avoids taking the coward's way out as his mentor David Chase did with the Sopranos.