As fundamental attributes of integrated energy systems (IESs), gas-thermal inertia and power-gas-heat interdependency significantly impact system resilience under extreme events. This chapter presents an integrated assessment framework that systematically examines these dual factors' impacts on IES resilience dynamics. The framework synthesizes three critical aspects: (1) operational constraints of the power distribution system (PDS), natural gas system (NGS), and district heating system (DHS); (2) multi-energy system interactions; and (3) gas-thermal inertial dynamics. A dynamic optimization model of energy flows is developed to replicate cascading failure progression and restoration sequences during extreme outages. Based on this, multi-stage resilience curves for the entire IES and its subsystems are derived. A set of interdependency metrics is further proposed based on the geometric features of resilience curves to quantify the vulnerability sensitivity of NGS and DHS arising from their interdependency with PDS. Comparative experimental analysis evaluates the impacts of thermal-gas inertia and system interdependency on IES resilience. Results indicate that the proposed metrics effectively evaluate the spatiotemporal interdependency among the power, gas, and thermal subsystems in terms of resilience, providing actionable support for operators to identify critical links and assess system upgrade strategies to enhance IES resilience.