Forgive me for editing your excellent post but I wanted to single out this section.
I completely agree that Betty's dream must be this kind of bizarre Mills and Boon fantasy in which she tries to make everything black and white, and where she is the victim, Don the evil husband and Henry her knight in shining armour.
The truth, of course, is rather more complex ...
Betty was quite right about having had a tough year but not all of that has been Don's doing. The ghost of her mother has always haunted her, and her father's death brought that all back plus a whole lot more. But Don has been pretty good throughout - he was the one who insisted Gene came to live with them.
I sympathise with Betty after Gene's death and Don's preoccupation with work (and, unbeknown to her, Sally's teacher) - but the answer to that isn't to fling herself at Henry so obviously. He could see it coming a mile off and knows exactly what buttons to press to get the results he wants.
However, what Henry really wants is, as you quite rightly point out, questionable. We have only seen him through Betty's rose-coloured glasses, so we know next to nothing about him. He has a daughter - but by whom? Where is her mother? Why did he and his wife split? Given what he does for a living and the slick manner in which he operates, I can't believe he is going to be all he seems. (Plus this is Mad Men, after all!

)
I do hope this isn't the last we see of Betty: her naivety neeRAB paying off. I can't see her asking Don for a reunion, but nor can I see her deluded editing of the truth leading to a happy ending.
I'm glad I'm not the only one who liked the Don/Peggy scenes. Like you, I can't see (and wouldn't want

) anything romantic to develop between the two of them, but they are so obviously kindred spirits, both trying to escape from pasts they don't want to define them. Don vocalising that obviously struck a chord with Peggy - and made for a really touching scene.
And yes, bring back Sal!