If a full 4 days has passed since you opend the case, you need to manually close it (it should go from saying sometyhing like "awaiting payment" to "receive fee credit" when you can close the case). Once you indicate that payment hasn't been received and close the case, the buyer will receive a strike on their account (not visible, but may stop them from purchasing from sellers who block buyers with 2 or more strikes), and your final value fee will be credited back.

You can then relist the item, if you wish.