TIL: If you use a Yubikey/Yubikey Neo as a gnupg smartcard, you can regenerate the secret key stubs with only the hardware token, provided you put the public key on a keyserver previously (e.g. at generation time).
1: Download Public Key
gpg --card-edit --keyserver pgp.mit.edu
fetch
quit
2: Regenerate Secret Stubs
Then, when you run the following command, it will regenerate the secret key stubs needed to decrypt or sign using the card:
gpg --card-status
3: View (Optional)
gpg --list-secret-keys