If he's storing his passkey in his password manager, it wouldn't matter that he lost the device. They can't get to it, it's AES-somebigassnumber-ed up the wazoo. If the passkey is cached outside of the password manager, then passkeys are a horrible idea, where you have to "go home and call the 800 numbers to cancel the credit cards", and worse still, people with few devices might end up in circumstances where they have no valid devices left to bootstrap access.
I am resigned to the fact that I will die with humanity never having solved the problem of passwords adequately, but being that I will live another two decades minimum, I will get to see two more of the stupidest possible non-solutions.
