You say that *you* haven't heard from *him* but have you tried contacting him again since then?
When you email, are you using a Hotmail or Yahoo account? You might be getting filtered accidentally as Spam.
eBay will give you additional contact information, such as telephone numbers, to make it easier to follow up on such matters. You may want to try that failing email.
Finally, email *does* get lost, and with the volume of business this guy appears to be doing, it could very well be that it just got shuffled off somewhere.