What happens if I lose my Yubikey and can't login?
Whenever you login with your Yubikey enabled, you are prompted to have your Yubikey use its authentication key to login. Underneath the entry field for your Yubikey, there is a link entitled
If you lose your Yubikey device, click here to disable Yubikey authentication.
Clicking this link will send an e-mail to your LastPass account e-mail address (or security e-mail address if you have set one), that will contain a link that will temporarily disable your Yubikey. If you are unable to access your e-mail for some reason, and have lost your Yubikey, please contact LastPass support.