Seized Brake Slider on VW GTI

Wife’s '04 went in for ABS warning light. She was told it was the central ABS module, but that the car could be driven perfectly fine (and safely) without it done right away. She came home to discuss it with me. Fast forward a few days, and the left rear brake slider seized. Now I’m out two new rear rotors, brake pads, and a caliper and slider set. My question: Is this something that should have been spotted when doing the original brake diagnosis? Would replacing the ABS central module when have prevented it?

Replacing the ABS central module would have had no effect. Corrosion caused the seizure. The problem may have been prevented by lubrication or if the mechanic had his crystal ball nearby.