Does the item still appear in your purchase history?If it does,then the listing has not been removed by eBay.The seller may have had an incorrect PayPal email address in his listing.This would cause the payment to show as unclaimed.
Try and contact the seller and ask that he add the email address to his PayPal account.This would have the payment show as completed.If youncan't reach the seller after a reasonable time,you can go to your PayPal account and cancel the unclaimed payment.
If the seller later contacts you,ask him to send you a corrected PayPal invoice,which you can then pay.
If the payment problem is straightened out,don't forget the 45 day time limit for opening an item not received dispute in case the item doesn't arrive.The 45 days are counted from the time you paid for the item.