High energy weapons can destroy mirrors.

Even if the mirrors are capable of reflecting the laser light, they likely unable to reflect two different wavelengths. So two high energy lasers would negate the mirrors effect.

Most of the mirrors able to reflect this are likely to cost more than the drones they would protect.

The best and cheapest strategy would be to fly the drones close to the ground. The closer they are the harder it will be for radar to detect, and lasers to target as there will be more obstacles in the path of the sensors/weapon.

Any sustained major conflict these high energy weapons make a significant impact will likely see drones quickly flying low on the ground. This will make it harder for automated systems to shot, but easier for soldiers with rifles.