Yes, Don Draper created the Coke ad. The last scenes of the series features Don hugging a stranger at a retreat and meditating with hippies before the episode cuts to the 1971 Coca-Cola "Hilltop" commercial. Viewers can infer that Don returns to McCann-Erickson and creates that ad. "I have never been clear, and I have always been able to live with ambiguities," said Weiner. "In the abstract, I did think, why not end this show with the greatest commercial ever made? In terms of what it means to people and everything, I am not ambiguity for ambiguity's sake. But it was nice to have your cake and eat it too, in terms of what is advertising, who is Don and what is that thing?"
Weiner knew the series' ending while wrapping season four. It's well known that Weiner disclosed Don's inspired idea to Hamm early on, but he also knew Betty's fate at that point too. "People die of cancer in the US. It's up there. I knew very early on. Her mother had just died in the pilot, and I knew this woman wasn't going to live long, and we love the idea of her realizing her purpose in life right when she ran out of time. ... I think there's a lesson to be learned about the randomness of things, and also she has some predisposition and some fairly seriously cancer-causing behavior."