On a 777 what would happen if the aft pressurization switch was accidentally left closed?
From my previous source in that incapacitation question:


  Two outflow valves are installed: one forward and one aft. Normally,
  most of the outflow is through the aft outflow valve. This improves
  ventilation and smoke removal. Cabin altitude and full ventilation
  rates can be maintained by either valve. Source