Omnichannel retailing has transformed the industry over the past decades by providing customers with physical and online stores. In this paper, we consider an omnichannel retailer with one online store and multiple physical locations. We explore the optimal product fulfillment and return policies in the face of supply chain disruption that leads to physical store closures. Insufficient inventory in the online channel creates challenges in fulfilling demand. To address this issue, we propose designating certain physical stores as inventory depots, playing the role of additional online stores. We develop a robust optimization model to optimize product fulfillment and returns, and to solve it, we design an algorithm based on constraint generation. Additionally, we conduct a sensitivity analysis to examine the model's responsiveness to various parameters. Our analysis confirms the effectiveness of this approach in enhancing supply chain resilience. The findings provide valuable insights for retailers to make decisions during supply chain disruptions.