"Okay," Don says with a resigned smile as he succumbs to the wishes of the Sterling Cooper & Partners partners. And with that, we're back in business.
In "Field Trip," Don both rebuilds and falls apart. In the first half of the episode, his marriage to Megan disintegrates as he comes clean to her about his job status. In the second, he's back at work, submitting to the strict rules that the partners set out for him. Their instructions mean he's not allowed to be alone with clients, has to stick to the script in meetings, and can only drink when it involves "client hospitality." Hence, Sterling Cooper will now have Don Draper without what made him Don Draper-y. He doesn't get to go off the cuff anymore, weaving miraculous pitches for clients. (When Ken Cosgrove shows Don a picture of his kid he says:
“That’s the carousel in central park, always makes me think of you.” New Don is a Don who can't give the "carousel" speech.) No more boozy, brilliant Don Draper. This is a Don that reports to Lou Avery. But Don, despite having another offer in his pocket, is willing to forgo the other aspects of his Don-ness to be back where he believes he belongs, Sterling Cooper. Unfortunately, Roger Sterling is the only partner who also thinks Don should be back at the agency. The other partners, including even Joan, are resistant. Might it have been better for Don to have taken the other offer? Yes. Would it have been as fun for the viewer? Not one bit.
Don is shaping up one aspect of his life while another comes crashing down. His admission to Megan of his status at the agency paralleled his season three admission to Betty of his past as Dick Whitman, one of the events that precipitated the fall of that marriage. "I couldn't risk all of this," he told Betty when describing the suicide of his brother Adam. Once again he blames his deceptions on keeping up appearances. "I know how I want you to see me," he explains to Megan. But whereas Don's truthfulness to Betty was tearful, his arguments to Megan are defensive, and she is loathe to give him any sympathy. “It’s okay, Don. This is the way it ends, it’s going to be so much easier for both of us,” she says.