When you sign up, the master password is used to determine the private keys and public keys. So you can derive all of this from your master password. Leave me with my master password stored on removable media. Then you can install another O/S on my computer. I could still recover and login to Hive so long as I keep that master password.
I had a similar problem and I couldn't remove my account from Hive Keychain so I removed Hive Keychain and installed it again. Then I could add my account again.