Allow users to resubscribe to cancelled parent subscriptions which have only cancelled resubscription orders. (Based on WooCommerce 3.0.11)

allow-resubscribe-cancelled-orders.diff

diff --git a/includes/wcs-resubscribe-functions.php b/includes/wcs-resubscribe-functions.php
index 2faea23..b8e94c8 100644
--- a/includes/wcs-resubscribe-functions.php
+++ b/includes/wcs-resubscribe-functions.php
@@ -219,11 +219,23 @@ function wcs_can_user_resubscribe_to( $subscription, $user_id = '' ) {
 			}
 		}
 
-		if ( empty( $resubscribe_order_ids ) && $subscription->get_payment_count() > 0 && true === $all_line_items_exist && false === $has_active_limited_subscription ) {
+		// When an order is cancelled, the subscription is cancelled.
+		// If all the resubscribe orders have payment cancelled and all the subscriptions have a status of cancelled then the user can resubscribe.
+		$resubscribe_order_cancelled = true;
+		foreach ( $resubscribe_order_ids as $resubscribe_order_id ) {
+			$resubscribe_order = wc_get_order( $resubscribe_order_id );
+			if ( ! $resubscribe_order->has_status( 'cancelled' ) ) {
+				$resubscribe_order_cancelled = false;
+				break;
+			}
+		}
+
+		if ( ( empty( $resubscribe_order_ids ) || $resubscribe_order_cancelled === true ) && $subscription->get_payment_count() > 0 && true === $all_line_items_exist && false === $has_active_limited_subscription ) {
 			$can_user_resubscribe = true;
 		} else {
 			$can_user_resubscribe = false;
 		}
+
 	}
 
 	return apply_filters( 'wcs_can_user_resubscribe_to_subscription', $can_user_resubscribe, $subscription, $user_id );

This diff is not quite correct and requires a check on that $resubscribe_order is indeed a WC_Order object before checking the status. See a slightly longer explanation here.