When healthcare resources become overwhelmed in medical disasters, as they inevitably will, we have to ask, in an unflinching fashion, the question: "What then?" or more precisely, "What should we do when we run out of resources?" In a mass casualty event worthy of the designation, we will indeed run out of resources, perhaps quite quickly. This article provides an ethical framework for the responsible management of medical disasters in which the "What then?" question must be asked. The framework begins with a critique of existing guidance from professional associations of physicians and then argues for an alternative approach that qualifies the obligation to preserve life, takes seriously the ethical challenges of overwhelmed healthcare resources, and countenances physician-assisted suicide as a last resort.