[Shoothe]

> Now I have one, but how do I handle the loss of one or more keys

The same way you handle loss of keys to your home, car, etc. - you buy a second pair. If you're using OpenPGP you can provision them with keys any time so it's not a problem but if you're using U2F then you better add at least two to all your services (Yubico has a cheap U2F only key).

[ben1040]

Yep. I got multiple U2F keys. One is on my keychain, another is in a drawer in my desk, and a third is in a safety deposit box at the bank with my other important documents.