How effective are formalized collaboration strategies when responding to a pandemic or disaster incident involving mass casualties and area-wide damage? How best can patients be transferred and resources, including staff, equipment and supplies, be shared across hospitals? ExtendSim was used to help quantify hospital system resilience to pandemic, MCI, and disaster events with damage. Patient flows through 9 critical units of multiple hospitals spaced over a large metropolitan region were analyzed to determine impacts on critical resources, physical spaces, and demand. Hospital resilience to these hazard events was evaluated to show the potential of strategies involving not only transfers and resource sharing, but also joint capacity enhancement alternatives to improve emergency health care service delivery through joint action.