If the user is no longer registered, you should be able to get your final fee back immediately instead of waiting for 7 days. If you need to contact eBay, the best way is to do Live Chat. I heard eBay phone support is awful. Live Chat should be able to help you.
Basically, your case is simple. The buyer is no longer registered. Don't bother to contact he/her to finish the transaction. You could get your final fee back immediately and then relist your item.