Can you think of some ways that an economy where virtually all the demand for goods theoretically possible is coming from 400 people, would see a substantial dr

Can you think of some ways that an economy where virtually all the demand for goods theoretically possible is coming from 400 people, would see a substantial drop in economic output? Assume everyone's participation in the economy aside from that 400 is limited to getting enough shelter that they don't die of exposure and enough food that they don't starve to death.