They provide a set of single use recovery codes for that purpose. I keep an encrypted copy of them in cloud storage and in several physical backups, so in the e

They provide a set of single use recovery codes for that purpose. I keep an encrypted copy of them in cloud storage and in several physical backups, so in the event that I lose or don't have access to neither my main nor backup yubikey, I can very likely still dig up a recovery code (eg by calling up a relative and asking them to read me the code).