Depends on the type of actuator; idling or non-idling. If idling, there is an internal idle circuit that ports the extend and retract side of the actuator cylinder together when there is no pressure. Such an actuator can be moved when something drives the surface while the actuator is unpressurized, and the fluid within will just circulate between the extend and retract sides. There is usually some restriction to this idle flow so the unpressurized actuator still provides flutter damping. You know an actuator has an idle circuit if the surface starts to sag part way over time when the aircraft is sitting unpressurized on the ground.
If the actuator has no idle circuit, and there is no extend or retract input to the servo control from the control system, it will be hydraulically locked at that position because the fluid on the extend and retract sides has nowhere to go (assuming the fluid isn't gone obviously). To move the surface of a no-idle actuator while unpressurized, you have to displace the servo control by moving the controls, which will connect the extend/retract chambers to the pressure/return sides of the hydraulic system to break the hydraulic lock and allow the actuator to be moved.
If there is a dual actuator installation with no-idle actuators and one of them is unpressurized, it will be hydraulically locked while there is no control input, but when you move the stick, the gang bar linkage interconnection of the two servo valves, that synchronizes them, will break the lock to make sure the unpressurized actuator doesn't resist the pressurized one.
With a dual actuator installation with idling actuators, when one is unpressurized it just becomes a flutter damper, and if both are unpressurized, the surface will sag on the ground or, if it was an aileron say, it would float up in flight.
A non-idle actuator would only sag on the ground or float up in flight if the control circuit itself is displaced to break the hydraulic lock that is set up whenever there is no servo input.
So if you have say a single no-idle actuator on an aileron while flying, and the pressure is lost, it will sit there at neutral, hydraulically locked there. If you were to move the control stick to displace the servo input, the hydraulic lock would be broken and the surface would float up. Normally they are in pairs so you'd have to lose both hydraulic systems for this to happen.
So, if the airplane you are concerned with has controls that sag when the airplane is parked, it has idle circuit actuators that would allow the surface to float or otherwise align with the stream, or sag if on the ground, if the surface was completely unpressurized. If the controls stay rigidly at neutral and can't be moved when the airplane is parked unpressurized (unless someone moved the stick while you push), it has no-idle actuators and they will stay at neutral in flight unless you move the stick.