The Rocky Mountain locust, Melanoplus spretus, is believed to be extinct. Habitat destruction via the conversion of montane river valleys to agriculture in the late 1800s is the currently accepted explanation for the species' disappearance. In the last decade, questions have been raised concerning both the status of the locust and the causes for its extinction. The paper addresses the arguments for and against M. spretus being extinct. Assuming it is extinct, new possibilities accounting for its decline are considered, including changes in forest ecosystems in the 1800s and the role of metapopulation dynamics. The loss of the Rocky Mountain locust provides a valuable test case for the tactics of rewilding. A benefit-cost analysis reveals that only under a narrow set of conditions would a restoration of this species or a proxy be justified. How the species might have persisted is considered, along with the possibility that M. spretus could recover. The roles of climate change and micro-evolutionary processes are evaluated with respect to the locust's return. Finally, the discovery of a surviving remnant of the Rocky Mountain locust would raise important questions with respect to our understanding of endangered species and how the concept of 'pest' pertains to conservation biology.