Word on the street is that Don Draper didn't experience personal enlightenment as much as he did a professional epiphany in that very last scene. It all boils down to the "Ping!" at the end and how you interpret that sound effect. Is it the peaceful hippie chime resonating across the rolling green hills of the spiritual retreat? Is the mental spark of an idea for the Coca-Cola ad that immediately follows Draper's smile?
I won't rule out the professional epiphany, but I feel it's secondary to Don's moment of clarity and peace at being in his own skin. He's the epitome of the antihero restored—and he didn't have to physically end his life to reconcile with the world. It's crazy how the entire series comes down to a single blip of a sound effect. Mad Men was such a great TV series. Here's to a successful show: Ping!