Toltol it's is not a fire warning.. And the light won't extinguish because you have filled the compartment with extinguishing agent... And there is no way for that agent to escape. Airbus specifically tell you the light will remain illuminated.
LAND ASAP
CABFANS..................................................... .........................................OFF
IF FWD (AFT) CRG CLOSED (displayed on ground only): Order the ground crew not to open the door of the affected cargo compartment, unless the passengers have disembarked and fire services are present. Also ensure that the FWD(AFT) cargo door is closed before discharging the extinguishing agent.
AGENT....................................................... .......................................DISCH
Note: Expect the SMOKE warning to remain after agent discharge, even if the smoke source is extinguished. Gases from the smoke source are not evacuated, and smoke detectors are also sensitive to the extinguishing agent.
ON GROUND BEFORE OPEN CRG DOORS: PAX......................................................... ........................DISEMBARK
BEFORE OPEN CRG DOORS (displayed on ground only): PAX........................................................D ISEMBARK