Would Joan have made the same choice — to sleep with the Jaguar guy — if Don had reached her in time? Maybe it would have made a difference to know that she hadn’t been betrayed by all her colleagues — that Don, at least, supported her. And surely the use of the flashback is intended to ask the viewer to consider the possibility of regret. But I’m not certain that Joan would have acted differently had she spoken to Don first. At the end of the episode, Don is alarmed and upset to see Joan walk into the partnership meeting, but Joan won’t acknowledge their earlier interaction, and is calm throughout. Ultimately, Joan makes a decision that is terrible and unsavory, but in light of the options with which she is presented and the turn her life has taken, it is also reasonable. I just hate to think of the nasty, smirking comments Pete will make about her when the opportunity arises.
Also — Seriously writers, we could have done without the Megan subplot. We get it.
And I admit it, I cried at the end.