delete_all_woocommerce_subscriptions.php

<?php
/*
Plugin Name: Delete All Subscriptions
Plugin URI:
Description: Delete all of those bad boys
Author:
Author URI:
Version: 1.0
*/
function mystic_delete_all_subscriptions() {

	$subscriptions = WC_Subscriptions::get_subscriptions(
		array(
			'subscriptions_per_page' => 1000,
		)
	);

	foreach( $subscriptions as $subscription ) {
		WC_Subscriptions_Manager::delete_subscription( $subscription['user_id'], $subscription['subscription_key'] );
	}

}
add_action( 'admin_footer', 'mystic_delete_all_subscriptions' );

function mystic_force_delete_subscription( $subscription_can_be_changed, $subscription ) {
	return true;
}
add_filter( 'woocommerce_can_subscription_be_changed_to', 'mystic_force_delete_subscription', 10, 2 );