The gas-thermal inertia and power-gas-heat interdependency, as two fundamental features of the IES, play a crucial role in IES resilience during extreme events. This paper proposes a comprehensive resilience assessment framework to investigate the influence of these two factors on IES resilience performance during extreme events. Considering the inherent operational properties of power distribution system (PDS), natural gas system (NGS) and district heating system (DHS), the interactions among multiple sectors and gas-thermal inertia, a dynamic optimal energy flow model is established to simulate the IES cascading failures and restoration process under outage scenarios. On this basis, the multi-stage resilience curves for the IES as well as each subsystem are obtained. Regarding the geometric features of the resilience curves, a set of interdependency metrics is further proposed to quantify the sensitivity of NGS and DHS vulnerabilities that arise from their interdependency with PDS. Comparative experiments are conducted to analyze the influence of gas-thermal inertia and system interdependency on IES resilience. The results demonstrated the proposed metrics can effectively assess the spatial and temporal interdependency among the resilience of power, gas, and heat subsystems, providing useful information for operators in identifying critical links and evaluating potential upgrades to enhance the resilience of IES.