Low brake fluid may damage your brake master cylinder and will cost you easily 300 up depends where you bring it to fix. 
I replaced Brake Master Cylinder couple years ago because clutch was not engaging well. Reason for clutch not engaging was the peddle needed a replaced but it worked well after getting weld.
This summer I had changed the rare rotor and caliper and full air bleed, should be okay for couple years.

As I knew the brake fluid was too low, I was afraid of brake master cylinder may need replacement. Luckily nothing  happen and working fine. From now on, I will keep my eyes on brake fluid reservoir ( restocked brake fluid). Thanks Sol.