From NPR, transcript here.
Michelle Scott is reading from the Common Core math standards for fifth-graders. She'll be teaching fifth next year, along with John Gries. And together, they're writing—and rewriting—lessons they'll need come September.
For the last sentence, did he want to say, “they're re-writing lessons they'll need if September comes”? He inverted the last part, put the verb “come” in the front and omitted “if”, right?
As far as I could determine, it seems only “if” with subjunctive voice could be used in this way. I don't think it's a subjunctive voice. In my impression, the subjunctive voice stands for those occasions when you're not sure whether it will happen or not, such as “If it were to rain, I'd pick you up.”
September will come sooner or later (it's not in limbo), so I'm wondering how to explain the sentence.