In this scenario, the project manager should engage in negotiations to address the conflict of resource allocation. The PMBOK Guide suggests that project managers should possess negotiation skills to resolve such conflicts effectively. By negotiating, the project manager can work towards a solution that satisfies the needs of the operations department while also ensuring the SME's contributions to the project are not lost, thus keeping the project on track.
References: The response is based on general project management principles as outlined in the PMBOK Guide and conflict resolution strategies that include negotiation, which are part of the PMP's body of knowledge.