All computers fail (ELAC, SEC, FAC, etc) and have no control with FBW system, under DIRECT LAW, still A320 can be flown by mechanical Rudder (directional control) and THS (pitch control). But still you need to have Hydraulics powered up or in both HYD and computer fail, the RAT will supply 3000psi to the Yellow system to power up the actuators of Rudder and THS. THS and Rudder have no direct end to end cable system but they controlled by cables which connected to a HYD actuators which ultimately control the surfaces.
Code0