Could vortex generators be used to preserve aileron authority during a stall?
Vortex generators re-energize the boundary layer and can slightly postpone flow separation at high angles of attack. Therefore, adding them in front of a control surface is a realistic way of retaining authority. In fact there are real life examples:



[picture by Peter Kämpf]

That being said, these devices are a crutch that is best avoided on clean-sheet designs. They add drag in every flight condition in exchange for some more margin at high alpha, this margin could be achieved by designing the aircraft better in the first place. That is why you will mostly see vortex generators applied as fixes late in the design process or as outright aftermarket modification kits. This constant penalty is compounded by the extra maintenance needed to keep the VGs clean and in good condition.

Ultimately, re-energizing the boundary layer can only do so much to prevent separation. A hard down aileron input at high angle of attack can stall the wing even with VGs, they are not a silver bullet.