You don't state in your e-mail whether you were communicating with the seller via eBay Messages or via an Item Not Received case. If you haven't yet done so open an Item Not Received case in the eBay Resolution Centre, and keep all correspondence with the seller exclusively via the case. If he or she contacts you via eBay Messages or via Private Messages in the eBay Community Forums, copy and paste the message into the case and then type your response, starting with something along the lines of "Further to your reply which you sent via eBay Messages, a copy of which has been included below..." as that way eBay can see all of the messages back and forth by just looking at the case details. They would still be able to access any messages the buyer sends to you via eBay outside of the case, but it would make it easier and faster for the eBay representative to work out what has been said, and by whom, if all of the messages were in one place.
In the event that you've already opened an Item Not Received case then should the seller become obstructive, or worse still, if he just completely refuses to reply to any of your e-mails, make sure that you escalate the case four days after the date that you opened it. That way you can ask eBay to step in and make a final decision upon the matter, in which case they'll more than likely force a total refund of the money that you paid to the seller.
Should something go wrong and it's either been more than thirty days since the latest estimated date of delivery, or if eBay decide the case in the seller's favour, open a case against the seller via PayPal. Unlike eBay, who only offer thirty days from the latest estimated date of delivery for buyers to open a case, PayPal allow buyers a maximum period of one hundred and eighty days during which to open a case against a seller. PayPal also tend to investigate cases far more thoroughly than eBay do, so unless the seller is able to prove beyond all reasonable doubt that the item was definitely successfully delivered to the address supplied on the PayPal confirmation of payment e-mail that he or she would have received when you made payment, then PayPal would decide the matter in your favour and refund your money in full.
In the event that you do have to go down the PayPal route to secure a refund make sure that you escalate the case to PayPal after two days but before the twenty day cut-off point. If you leave it any longer than twenty days and then try to escalate the case you will not be able to do so, in which case you'll have no means of being able to open another case in order to get your money back.
