When I first watched it, I actually interpreted it the complete opposite way. That while the entire show was based around Don's character, and how the universe seemed to revolve around him, all of the moments he chose to disappear (whether from work, from his kids' lives, from himself) pretty much amounted to nothing. Don was supposed to be the driving force behind this revolutionary Coke ad campaign, but instead, he chose that time to disappear and go on a self-imposed hiatus. However, while he's gone, the world continues to spin (Sally can handle things without Don, Peggy finally finds what she's been looking for, Sterling finds his next source of happiness, the firm continues to be just fine, Coke still comes up with a fantastic ad campaign) as if his presence wasn't really necessary at all. He carried himself like Zeus Almighty, and wanted to believe that everybody and everything would collapse without him, but that was clearly not the case. Hence his existential crisis...... However, after reflecting on it, I think your interpretation falls more in line with the rest of the show's theme. While Don deviates from his path periodically, at the end of the day, he doesn't change. And even though this last deviation was more prolonged and pronounced, at the end, it's what gave him the enlightenment to come up with the best ad campaign of that era. Some things never change.
I'm super late to this party...but my wife and I finished watching Mad Men about two weeks ago, and it's among my very favorite shows of all time. Maybe my favorite. I was sad when it ended that we didn't have another episode to watch.
