Send to customer and 'CC' the admin on sub expired emails

add_recipient_sub_expired_email.php

<?php
/**
* Plugin Name: Sub Expired Email Send to Customer
* Plugin URI:
* Description:
* Version: 1.0
* Author:
* Author URI:
**/


add_filter( 'woocommerce_email_headers', 'sub_expired_email_add_admin_cc', 9999, 3 );

function sub_expired_email_add_admin_cc( $headers, $email_id, $order ) {
    if ( 'expired_subscription' == $email_id ) {
				$email = get_option( 'admin_email' );
        $headers .= "Cc: Admin <" . $email . ">" . "\r\n";
    }
    return $headers;
}

function sub_expired_email_recipient( $recipient, $order ) {

    // Bail on WC settings pages since the order object isn't yet set yet
    $page = $_GET['page'] = isset( $_GET['page'] ) ? $_GET['page'] : '';
    if ( 'wc-settings' === $page ) {
        return $recipient;
    }

    // just in case
    if ( ! $order instanceof WC_Order ) {
        return $recipient;
    }

    $email = $order->billing_email;

    $recipient = $email;
    return $recipient;
}
add_filter( 'woocommerce_email_recipient_expired_subscription', 'sub_expired_email_recipient', 10, 2 );