We received a letter in the mail, completely unsolicited, telling us that we’d been granted an appointment at the Ausländerbehörde to extend our visas. This threw us a bit — did we have to show up? We had no intention of staying longer than we’d originally stated in our visa application.
Short answer: No, you don’t have to attend the appointment. We emailed the Ausländerbehörde to let them know we were leaving before our visas expired. A week or so later, a letter arrived in the mail informing us we were under no obligation to attend the appointment.
Maybe sometimes the Germans are a bit too proactive!