What should you do when an employee resigns?

What's Really Going On: A solid performer resigns. What's often been going on?

Problems with their manager or growth that went unsaid. People often leave managers and stalled growth as much as companies. Source: Wikipedia – Employee retention

What To Do: What should you do?

Thank them, plan the handoff, and ask what would have kept them. Honest exit input is your best data for keeping the rest. Source: Wikipedia – Exit interview

Why It Works: Why does it work?

A graceful exit protects the team's morale and your reputation. The remaining team watches how departures are treated. Source: Wikipedia – Employee retention