PayPal Standard that comes with WooCommerce should be updating itself already when orders are completed. At least it was doing that last time I played with it, but I don't typically use it, so maybe it has changed.
PayPal simply does not offer "guest checkout" to all people in all countries. There are a number of variables involved. Express Checkout does allow you to force the guest checkout experience regardless of any cookies that are set (which is one of the primary reasons people upgrade to Express Checkout over Standard) but it still does not guarantee that all users will have the option.