Gas-insulated substations and switchgear (GIS) offer compactness, reliability and environmental protection, but the continued use of sulphur hexafluoride (SF6) creates a material climate-management obligation because small losses can dominate the greenhouse-gas footprint of otherwise efficient high-voltage assets. This review develops an integrated low-carbon operating framework for Saudi GIS portfolios by connecting four practices that are commonly managed separately: leakage detection, gas recovery and inventory control, predictive condition assessment, and risk-based asset-life extension. A structured integrative review of peer-reviewed research published from 2020 to 2025 was conducted across recent SF6-alternative, leakage-monitoring, partial-discharge, digital-twin, health-index and lifecycle studies. The evidence indicates that decarbonisation cannot be reduced to replacing the insulating gas. Existing fleets require accurate leak localisation, closed-loop gas handling, condition-informed interventions and disciplined decisions about refurbishment versus replacement. Infrared and multi-channel optical methods improve non-contact leak identification, while decomposition sensing, vibration analysis, partial-discharge diagnostics and data-driven models broaden the observable condition state. Health-index and condition-based risk-management methods then translate heterogeneous evidence into maintenance priorities and life-extension decisions. For Saudi Arabia, the proposed architecture is designed for hot, dusty, geographically dispersed and rapidly modernising grid environments, where outage avoidance, technician capability, spare-parts strategy and emissions stewardship must be considered together. The review concludes that smart GIS should be governed as a coupled carbon-reliability system in which gas balance, defect evidence, intervention history and remaining-life decisions continuously update one another.