A customer has given excellent feedback on the project, but a key project resource is leaving the company. Which measure should mitigate the impact of this resource's departure?

Establishing a proactive knowledge-sharing plan is the most effective measure to mitigate the impact of a key resource's departure. This ensures that critical information, processes, and expertise are documented and transferred to other team members before the resource leaves, minimizing disruption and maintaining project continuity. Offering a new contract might retain the resource, but it's reactive and doesn't address the underlying risk of single points of failure. Allocating a contingency budget for replacement is a financial measure, not a direct mitigation of the knowledge loss. While updating the risk register and informing the customer are good practices for transparency and risk management, they do not actively prevent or reduce the operational impact of the resource's departure.