Lockheed had a rule-of-thumb that widebody production was not profitable once you fell below 2 a month. Boeing fell below this a while ago with the 747 (they only did 3 passenger 747s in the whole of 2004, although several more freighters).
However aircraft components are often ordered from suppliers in batches, and there may well be 10, or 30, or whatever number of sets of parts still in the pipeline, to be paid for on delivery but subject to penalties if cancelled. It's when the remaining number are sold that decision time will arrive. Plus Boeing presumably want to keep Everett going (it also does the 777 and he similarly-orderless 767) until the 787 production gets going.