Auto send message to email of user which account is being Deleted(You can change the message as suit you)

function myb_delete_user($user_id) {
global $wpdb;
    $email = $wpdb->get_var("SELECT user_email FROM $wpdb->users WHERE ID = '" . $user_id . "' LIMIT 1");

     $headers = 'From: ' . get_bloginfo("name") . ' <' . get_bloginfo("admin_email") . '>' . "\r\n";
     wp_mail($email, 'You are being deleted, Mate', 'Your account at ' . get_bloginfo("name") . ' is being deleted right now.', $headers);
}
add_action( 'delete_user', 'myb_delete_user');