Well, lost or stolen hopefully wouldn't happen if it's embedded in my hand—that's the point of embedding it in my hand!

To protect against damage—which is a very real possibility, of course—I'd put identical chips in each hand, and if one fails or gets damaged, then you'd have to rotate keys by replacing both chips.

And you could have a third identical chip/key (or a different private key on another device in a safe somewhere) as a further backup, as my sibling comment recommends.