Our study focuses on sustainable dye wastewater management through catalysis, scrutinized by surface-enhanced Raman spectroscopy (SERS) using an ecofriendly magnetic nanocomposite (Fe3O4/SiO2/Ag (FSA)). To our knowledge, the use of green synthesis for fabricating nanocomposites from a single source, namely Nerium oleander leaves, has not been extensively explored. This poses a distinctive and challenging approach, differentiating it from conventional chemical methods. Analytical investigations confirm the nanocomposite morphology, featuring Fe3O4 cubic cores with SiO2 spheres and silver nanoparticles (AgNPs) decoration. Efficient catalysis rapidly degrades unary and binary dye systems (MB, RhB, and MB + RhB), with high efficiency in short durations (MB: 96% in 10min, RhB: 94% in 2min, MB + RhB: 96% MB and 91% RhB in 9min) and with elevated "k" values. SERS monitors water quality, revealing complete degradation and quenching of dye fingerprints with fabricated nanocomposite FSA. The nanocomposite exhibits reusability over four cycles by easy recovery of catalyst with external magnet. The nanocomposite achieved 89.7% degradation efficiency in real-time household wastewater treatment. The proposed research aligns with UN SDGs 6 and 15 and this approach holds promise for advancing industrial waste management.