The slow but steady disintegration of Don Draper continues as his tenuous relationships fragment and falter. That's been the theme all season long, and the writers are not stepping back from that abyss. If anything, we are beginning to see Don's first hints of awareness of the fact, as he drunkenly attempts to apologize to Allison for his behavior.
Of course, that would approach something genuinely felt, so that simply isn't going to happen. Don is still trying to maintain the image of the man in control, at least in the office, but he is not going to last long at the rate of his current descent. If nothing else, his liver may not be up to the task, despite the many years of preparation.
The episode focuses just as much on Pete and Peggy, if not more, and it's an interesting bit of overlap. Pete's maneuvering and family successes are eerily similar to Don's own past choices, but without the creative instincts and legendary business acumen (which Don himself is lacking of late). While Pete may not have the identity issues that Don is dealing with, he is still modeling himself off of Don and others, and the end result threatens to be the same.
Peggy, on the other hand, is getting wrapped up in some of the social revolutions of the day, which is a nice callback to some of her more progressive character aspects from previous seasons. Naturally, everything that is happening with Pete brings up their past relationship, and it likely prompts some of her behavior with Joyce and her gang.
While it has been on the periphery, this is a nice way to explore Peggy's character evolution while also providing the necessary glimpse into the social shifts taking place. The decision to break out into a new agency with evolving methods and attitude may itself be a metaphor for the historical shifts about to explode on the American consciousness. And considering that those changes did not come easily or without price, this casts a foreboding shadow over the challenges to come. All of which, of course, is also a reflection of Don's tortured journey.