The night vision goggles people generally think of consists of a microchannel plate with a phosphor screen at one end – it’s essentially a small TV camera, and you’re looking at the screen. As such, it will certainly protect your vision, since you’re not looking at the outside world.
Unfortunately, it will protect you by taking the hit. A laser beam on the sensitive end of a night vision system will at least “dazzle” it and, if strong enough, damage it. So, unless you have a replacement, you’re blind again, unless you risk your own eyes. Of course, if you do have a replacement, you can continue to use it, until it, too, isd blinded.
The obvious solution is to have a protective screen to protect the night vision system from lasers – but that’s just what you want in a pair of laser protection goggles in the first place. If you had that, you wouldn’t need the Night Vision goggles.
Proper laser goggles are normally specified to work only between certain wavelengths, and are quite expensive. And I can tell you that a significant portion of a visible laser beam will pass right through a normal mirror, and so a pair of mirror shades would offer very little protection.
As for the power of the laser, it’s the optical power density that really counts. A 10mW laser with a beam area of 5 square millimetres will be about as bright as strong sunlight, or 2000W per square metre. Getting a flash of this in your eye will do more damage than staring at the sun because the limited size beam doesn’t trigger the pupil constriction mechanism until it’s too late.
Eye damage by laser is more of a cumulative effect; a building up of small blind spots that initially go unnoticed, a bit like with welders’ arc-eye.