MonoBehaviour.OnDisconnectedFromServer(NetworkDisconnection)

Description

Called on the client when the connection was lost or you disconnected from the server.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    void OnDisconnectedFromServer(NetworkDisconnection info)
    {
        Debug.Log("Disconnected from server: " + info);
    }
}