When Jared Harris, a.k.a. the late Lane Pryce, suggested that Elisabeth Moss would not be returning to Mad Men, he was called out for his loose lips, but covered his tracks saying, "I have no idea what Matthew Weiner intends to do." Matthew Weiner, however, does know what he intends to do, and he's now publicly stated that Moss will return next season.
In an interview with TVLine, Weiner said, “When people leave Sterling Cooper, sometimes it is the end for [the character]. But I will spoil that one tiny piece of anticipation and tell people that Elisabeth will be showing up to work... I can’t say how much, in what capacity or what [her story] is going to be, but she has not left the show.”
The sixth season of the show will go into production later this year, and THR says Weiner "is confident that the option for a seventh will be picked up." After that, it's all over... and if you remember, Weiner already somewhat spoiled the big ending.