We don't have to worry about spoilers anymore, so removing the North American Aviation look.
Just watched again and trying to sort out the meanings of the episode title. Good call on Bye bye Birdy, meaning Don to Birdie. He is emotionally detached from her and his eye is roving again.
Love, among the ruins of Don's marriage appears in the form of Suzanne at the end. He surreptitiously makes physical his felt connection to her, through the grass at their feet.
The Bye bye song is sung by Peggy to herself in the mirror, too, acknowledging her broken connection to Pete, and her bittersweet musing that she'll always care, nonetheless.
Peggy also seeks love of sorts, among the ruins of New York, a city in decay, as illumed by the trash on the subway steps as she emerges to the crowded bar. She connects physically with her one night stand, but the passion is tempered by practical considerations. He doesn't have a condom, but they can do other things. She has to work in the morning, and leaves in the middle of the night, as soon as he's fallen asleep. Her true love is of her job, a problem that recrudesces in The Suitcase.
The last scene of Don and Peggy at work puzzled me the first time I saw it; seemed a bit flat. But that's what it was trying to convey. Peggy's personal life is a bit of a ruin, and she loves the excitement and challenge of her job more than she does any human.
And the same could be said for Don, despite his upcoming hard fall for Suzanne. This conflict was expressed in his fight with Faye in the Chinese Wall episode. What she called his "stupid job" was everything to him. Whether future human agents of true love emerge for either of them, or mere secondary objects of lust and infatuation, time will tell.
Edited by Tom Bomb, Dec 22, 2011 @ 8:18 AM.