Hi there!
When a PC is "OUT", the fiction will tell if:
-- An Assistance will be needed just to enable them to act (e.g. a teammate that drags them out of the building)
-- Assistance will ALSO add a die to their roll if it mitigates the severity of the injury (e.g. a teammate helping the almost blind PC with navigation while hacking traffic lights during a pursuit)
Either way, the PC who is assisting will have to spend 1 Stress.
And yes, an Overloaded and Out PC is in big trouble and will need assistance or find a way to Take a Breather to recover some Stress.