Maybe he wants the deceased animals back. If you don't know the "Gentlman" well, then it stands to reason he does not know you well and may need to verify the animals he thought were healthy actually died. Could all be an honest misunderstanding. I'd tell him you will gladly pay shipping to return the deceased bodies (I imagine you can use regular USPS if you wrap them well, after all, no worry about them dieing now, they already did) but that you will expect him to foot the bill for replacement animals. But only if they died the day you got them. If you had cared for them for any amount of time it would be different.
<img src="http://www.faunaclassifieds.com/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt='
'> Just my opinion~ Take it for what it's worth, not much!