Allow customers to download all files associated with a product to which they have purchased a subscription - even after their subscription has been cancelled or expired.

wcs-perpetual-download-access.php

<?php
/**
 * Plugin Name: WooCommerce Subscriptions Perpetual Download Access
 * Description: Allow customers to download all files associated with a product to which they have purchased a subscription - even after their subscription has been cancelled or expired.
 * Author: 
 * Author URI: 
 * Version: 1.0
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 	
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @author		Brent Shepherd
 * @since		1.0
 */

function eg_allow_perpetual_downloads() {
	remove_action( 'woocommerce_order_is_download_permitted', 'WC_Subscriptions_Order::is_download_permitted' );
}
add_action( 'plugins_loaded', 'eg_allow_perpetual_downloads' );

Based on my testing, it appears that this mini-plugin no longer works because is_download_permitted is now deprecated.

I created this Gist, which was tested with WCS v. 2.5.2 and appears to work correctly to expand download access to subscriptions with the status of Expired and Cancelled: https://gist.github.com/jessLundie/603d9ef96f6c0d8fc01662fdd1acd3ac