Don couldn't have fired Pete for what he did with Joan. Pete's a partner and they'd have to take a partner vote to boot Pete, and we already know how that vote goes. I don't think Don is a saint by any means, but I don't think he was being superficial by stopping by her house. His ego is so big he thought the discussion was over when he left the room--he thinks he's that important and nothing further would be done, let alone a partners' vote. Sure, that means he was butt-hurt at being ignored and that was no doubt part of the reason he went to Joan's place. But I still believe he has respect for Joan; how many as hot as Joan women on the show has he NOT hit on?
As for Joan actually going through with the deal, as degrading as it is, I still think at least it was on her terms and wasn't as horrifying to watch as Dr. Greg raping her in Roger's office, then her marrying the asshat, and then having to perform on the accordion for his doctor advisers, like a trained monkey. (In case it's not clear, I think Greg is THE worst. Well, neck & neck with Pete, at any rate. )
It made me so happy to see Freddy again! He's still sober, still working, and still a good pal to Peggy. Peggy's departure scene (while excellently played by Moss & Hamm) was, for me, Don being the bigger ass than even with his little snit fit with Megan & her Boston preview possibility. Megan decides to leave the job to pursue her acting career and she gets a lunch with the girls. Peggy doesn't get so much as a box to clean out her desk. Yeah, she was going to a competitor, but if Don hadn't taken her for granted for so long, it wouldn't have come to that. Almost bringing up the baby incident from now ~6 years ago and then that lingering hand kiss...it was just one weird scene.
There was something off about the timeline. In the last episode, they were going to work every weekend through Christmas on the Jaguar campaign. What did they do during all that time if it was just a few weeks before Valentine's Day and they had nothing to show for it? And going a bit meta for a minute, it's just odd that both Hamm and Slattery do car ads IRL.