The stakeholder has notified the project manager that new priorities have caused them to shift all of the business subject matter expert resources to a new project for one year. The BEST course of act

A phase gate review is used to evaluate project performance and determine if it should proceed to the next phase, which is not the primary action when a fundamental resource dependency is completely removed.

The absence of all business subject matter experts (SMEs) for a full year due to shifting stakeholder priorities represents a critical resource constraint that likely renders the current project impossible to complete or severely compromises its objectives and timeline. In such a scenario, the most pragmatic and responsible action for the project manager is to recommend project cancellation, formally documenting the reasons and the impact on the organization. This allows the organization to reallocate remaining resources and focus on projects that are viable.

Project completion implies that the project's objectives have been met, which is clearly not the case when all critical SMEs are removed for a year.

Stage completion refers to finishing a specific phase of the project, but the issue described affects the entire project's ability to proceed, not just the completion of a stage.