To have the season end with Megan's murder would fit in the narrative of the rising crime problem in New York City, from the intruder in the Draper home to the ambulance sirens that can often be heard from the Draper balcony. It would also explain what the cop cars are doing in season 6's promotional poster.
Megan is already dead
Going one step further, super fan Dustin Rowles at Uproxx postulated Megan is already dead, and it is her ghost Don sees in his hash hallucination during the most recent episode. Even though she appears in the previews for the next episode, Rowles points out the possibility here too she could be only in Don's head, and the black and red outfit she wears is symbolic of a violent death.
Don will die
Over at Slate, Seth Stevenson takes the Megan-death theories, and raises it with a prediction that Don will be dead by season's end. He points out the death imagery follows both the Drapers – not just Don. But he doesn't do much to flesh out of the idea, other than arguing that it would appeal to creator Matthew Weiner's style: "How Weinerian would that be? Icing the icon of your show seems like the sort of zagging – a rebellion against TV's established order, if you will – that Weiner can't resist."
If that's the case, then what will season 7 be about? Everyone at Sterling Cooper waxing on about his legacy? (Aside from some clever ads, there really isn't much, when you think about it.) The truth about Don's identity switch? Sally going full throttle into teenage rebellion?
If "Mad Men" could be understood as the life and death of the 1960s, and Don Draper the observer-participant in America's transformation in that period, then his death in season 6 would make season 7 a eulogy for the '60s – not the craziest idea. At least not as crazy as the theory that the whole series is just a story written by Ken Crosgrove.