If there is a seventh season of "30 Rock," or if NBC hasn't completely lost its marbles by deciding their shouldn't be one, or if the world has not come to an end by then (it is 2012 after all), in which case there will not be another season for any new show, then Alec Baldwin will be returning to the classic series.
Tina Fey confirmed this on "Letterman" last night, and while it's certainly been hinted at in other places, this seems to me the most solid declaration yet. [Update: NBC just made the formal announcement in LA at the TCA. He'll be back for the 7th.] Baldwin -- he who plays with words on planes -- has himself hinted at all sorts of things over the past year or so: Like, he might run for office, or he might quit show biz, or he would probably quit "30 Rock," or something. But clearly "30 Rock" without Baldwin would not be "30 Rock."
Seriously, will there be a seventh season? I guess it's best to ask that question at the end of the sixth, which begins next Thursday, but if Tina Fey wants one and Lorne Michaels wants one, then I imagine there will be one.