LUKS is full hard drive encryption. If you encrypt your entire hard drive with a yubi key, then lose the yubi key, and you have no backup, you’re shit outta luck. I encrypted my hard drives with a USB drive in a similar fashion. Then made backups of the USB drive, so that the scenario I describe wouldn’t happen. Hopefully. It’s kind of like horcruxes. If somebody steals them all, I become mortal again. Actually, though, if somebody steals them all, I lose all of the data on the hard drive.