the juxtaposition of Peggy and Joan shows the extreme contrast of what the two women had to do to finally attain a level of power where they would be seen as equals as the men in authority
the two stand for the ideal women of that decade: Joan for the 50s to early 60s trophy women who were expected to be beautiful, take care of families and the daily operations of offices if they were working (SC and SCDP were in a sense Joan's family) and Peggy for the young and empowered take-charge women of the mid to late 60s who strove for independence and equality in the midst of the feminist movement during that time
Joan had to use her body as the means to finally attain power with the company she's been working for for years while Peggy used her brains and talent to break free from Don's control and be her own boss in another company
both had to give up something (Joan some of her dignity and Peggy her longtime relationship with Don whom she saw as a friend and mentor) and they struggled with it but they got over quickly (which in the case of Joan is somewhat admirable as she understands power no matter the cost is exactly what she needs considering her personal situation)
i'll have to check again what you were referring to about that door opening thing
Roger is definitely nearing the end of his "utility" in the office but i highly doubt that he'd take his own life willingly
we might see him wasting away his years in an alcohol and/or drug fueled haze banging all sorts of women half his age but i don't see him as the kind of guy to go out on one grand act of suicide
or maybe he'll just be happy carrying on his affair with Megan's mom without a care in the world till he dies of a heart attack or lung cancer in his 60s
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all you need