Actually, if the system fails, the "reduced braking" warning will be displayed, in RED, on the cluster. Anyone who has ever experienced this (it's happened to me twice) will agree that there is indeed much greater effort required to stop the car!

When the hydraulic unit has nearly reached the end of it's service life, or "times out", "Service Brake/Visit Workshop" is displayed in white. In this case a fault code is stored in SBC, instructing (as per SDS) the tech to check the operating time of the hydraulic unit. After this check is carried out the tech is then instructed to either update the SBC software, or, replace the hydraulic unit.

I hope this helps explain how the SBC system works.