“Mad Men’s” riveting, immensely satisfying finale reboots the franchise as it heads into — can’t wait — season four. Sterling Cooper is over. Don and Betty’s marriage is over… or so it seems. Series creator Matthew Weiner wisely set the country-shattering JFK assassination in last week’s episode, getting it out of the way, so he could focus on Don Draper and the core story. Big events dropped in a swiftly-paced hour (thanks for the limited commercial interruptions) that included strong emotion and light humor (Roger got the best lines as usual). Don comes out of his twin traumas with a renewed sense of confidence and a hopeful future. He’s part of a new ad agency, and, personally, I think, he’s better off without Betty, the spoiled brat-woman who can’t find happiness. Will Suzanne return, or will there be some new women in his life? It will be interesting to see where Weiner opens the new season, hopefully not too far in the future so we can see Sterling Cooper Draper Pryce get off the ground amid the backdrop of the changing times of 1964-65. P.S., January Jones hosts this week’s “SNL,” and wouldn’t it been fun to see Jon Hamm make a cameo.