Network.OnDisconnectedFromServer(NetworkDisconnection)

Description

Called on client during disconnection from server, but also on the server when the connection has disconnected.

When called on the client the connection was lost or you disconnected from the server. The NetworkDisconnection enum will indicate if the connection was cleanly disconnected or if the connection was lost. When called on the server the connection has successfully disconnected (after a call to Network.Disconnect).

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void OnDisconnectedFromServer(NetworkDisconnection info) {
        if (Network.isServer)
            Debug.Log("Local server connection disconnected");
        else
            if (info == NetworkDisconnection.LostConnection)
                Debug.Log("Lost connection to the server");
            else
                Debug.Log("Successfully diconnected from the server");
    }
}