I get these "pended" claim notifications from Blue Cross and Blue Shield fairly regularly. As soon as I get it I send the patient a letter informing them that they need to take care of it or they will have to pay the bill. I always include a copy of the notification AND the phone number and their ID# so that they're prepared to take care of it. Response is usually fairly good.
If the patient doesn't take care of it, and the insurance denies the claim due to their non-response, they get the bill.