Demand increasing from factories is nice and all, but as it is eventually you hit retail goods which aren't always sold so fast. As retail goods supplies increase, the demand for those items on the current market decreases (since retail companies won't buy what they have too much of) and causes a wave of saturation back across the supply chain. And while this could maybe be mitigated by increases in the numbers of goods, the rich are now so rich they can easily jump into any new markets and quickly saturate them as well. Technically, if producers would lower the ridiculous profit margins, retail could too, creating more incentive to go into retail as a nonsupplier and meaning more goods are sold (for less), keeping the economy moving at a brisk pace. I'm really more worried of a stifled economy at this point.
Hence the idea of pop growth:
Population growth could be tied to overall saturation. As people have more stuff (that is, as overall markets become more saturated), growth increases. If big companies quit the game and overall saturation immediately takes a big hit, population growth slows... or even decreases... to match the overall average saturation level of products. This ensures that some markets stay saturated, but prevents ALL of them from it like some in the thread are worrying about. I'm not sure how well it would work, so I shan't be pitching it in the suggestion forums until I mull over it a bit more. It'd be a fairly sizable change to the game, anyway.