The new, final season began last week shrouded in so much mystery, it was challenging to even discuss it. But now, a week later, a few elements are fair game. One is that this final season has resumed near the end of 1969. Another is that Don’s wife, Megan (Jessica Paré), is up for a part in that glamorous 1969 TV trivia answer, Bracken’s World. And a third is that Don is surviving, for the moment, by getting a former associate to pitch his ideas, serving as a front. What happens tonight? No idea. AMC sent out only the season opener for preview.