Hello Masterhelwan,
Just to clarify. You are talking about a "faulty aileron" being taken over by a "stby aileron", or are you talking about the aileron actuators?
All Airbusses I flew don't have active and stby ailerons, only active and stby actuators. (depending on type the difference is there hydraulic, or elec source for actuation)
The actuators can be faulty. Dispatch according to MEL is allowed as long as the other actuator is available. This should answer the question as the requirement does not allow you to dispatch with both actuators faulty = aileron faulty.
Hope it sheds some light.