More clues Don Draper will die at the end of Mad Men are in 702, "A Day's Work". When Don is at the restaurant with his daughter, he asks her how her studies are, and her one word answer is "Spectacular", just like in "American Beauty" when Lester Burnham asks his daughter how school was. We already know from the start of the film that Lester will die.
I have a feeling the tone at the end of Mad Men will have a similar feel to the one in American Beauty, and that "spectacular" was a reference to the movie.
Pete says "No one feels my existence" and Ted responds, "Just cash those checks. You're going to die one day."
And, of course, Sally goes to NYC for her roommate's mother's funeral and ends up spending time with Don because she lost her purse. Talking about the funeral, Don tells Sally, "I'm sorry you had to see that." and "Life goes on." Her response is "I'm so many people." Cryptic. Their visit ends with her telling him "Happy Valentine's Day. I love you."
The song at the end is "This Will Be Our Year" by The Zombies.
It may be Don's last year on earth.