While I do agree this is technically a case of user abuse/error, I have read about too many stripped threads, and screw heads, on the D25s, including the one I recommended to a friend. To me, it kind of points to design problems (inflexible steel clips requiring user intervention, proprietary hex sizes, and thin-walled attachment points). ET doesn't HAVE to repair it under warranty, but as act of goodwill, I think they SHOULD.
In another good example, Foursevens Mini AAs have a very thin split-ring attachment point that tends to break after a couple years of key-chain carry. From the reports I've read, 47s simply mails out a new body if you do break it.
JMHO, it may not be worth the cost or time mailing back to China anyway, but maybe send a kind email to them and they might just mail you a new tailcap piece
.