If someone can login as root on that machine, by for example rebooting in recovery mode, they can also run the script and access the drives. Or they can get the password from the keyring. A keyring that doesn’t require a password to unlock or whose password is stored somewhere on the machine is equivalent to plain text storage. There’s no obvious solution other than ensuring the system can’t be rooted without a login, I’m just pointing the flaw out in case you feel it’s more secure than it is.
wesker