http://www.avclub.com/articles/lates...be-just,98653/
^ new theory that Megan is actually already dead. That sort of thing doesn't fit this show, and would rely on next episode picking up right where this past one left off, which never happens on Mad Men. Still interesting to read. I will be absolutely shocked if Megan survives the season with all of the imagery they have been piling on lately. I think that if anything Don's hallucination of Megan in California represents the death of his ideal of her rather than her actual death.
I agree, I think it's going to be the ideal. They are really dog piling on the "Mother" themes/symbolism, emphasizing how much Don wants that. And if you think to the Season where Don fell for Megan, she seemed like the perfect mother figure. I think this is all going to culminate in him finding out she had an abortion, and then he's going to split with her and slowly after that "Don Draper" will die, and he will become Dick Whitman again.
As for him being dead? California is always used to "kill" Don Draper--think about every time he goes there. He instantly reverts to Dick Whitman and considers abandoning his life as Don Draper. The first time he runs off with all those rich people, and a girl named "Joy" that promised him eternal happiness? The next time he contemplates staying to help Draper's wife with cancer, and is only forced to leave by her sister. The next time he falls in love with the "ideal" of Megan and how she is absolutely (unrealistically) perfect in every way. California has always represented "heaven" and the death of all the falsehoods he's built up in New York.
So when Megan says "I live here"--She meant that Don's version of her, the version Dick Whitman fell in love with, the mother (Hence the belly), and free, independent spirit, lived there. The Megan back home is Don Draper's wife--it's the person he doesn't know. (This week he even says I usually feel better after being out there--I think that has to do with how this time he wasn't able to kill of Don Draper as much. Also this week he even said "that's not my name" when the lady called him Don.)
Just my guess anyway. Maybe the guy is right and it's more literal. There is some compelling evidence of it--like the phone call/sharon tate ect. But I think it's more symbolic. I think Roger's words at the end were carefully chosen too--"New York is the center of the world", the real world, reality. California is Dick Whitman's heaven.
I wouldn't be surprised either way, at all. Literal death or figurative would both fit with the symbolism thus far. I just have a feeling it will be the figurative death because of all the "motherly" themes that have come up. If it is literal though, I think it's going to be Bob Benson who does the killing.