B777- In emergency mechanical back up how does the flight controls manage engine failure In case of engine failure above the ocean with multiple electrical failures and after having exhausted the batteries the fly by wire mechanical backup with available hydraulics if left with the THS and one spoiler per wing under the control of the control wheel, How in these conditions the pilot will manage the asymmetrical thrust?

Basically thrust asymmetry is normally managed with the rudder, the schematic shows in mechanical backup the rudder is not Available, while the remaining spoilers 4 and 11 are rather for roll control, what can do the pilot?

N.B. June 17, 2019: if it is difficult to imagine one engine failure + total electrical failure, please imagine an engine failure + Total FBW computers and controllers failure, the most important is to go into the mechanical mode as described here below with an engine failure:
In your scenario there would likely still be hydraulic power and electrical power from the one running engine and the RAT (Ram Air Turbine) generator, which can power everything except the autopilot. The TAC (Thrust Asymmetry Compensation) system would compensate for the asymmetric thrust.