Torus's OAuth logins inherits account recovery and management mechanisms of existing account management systems (eg, Google's password recovery system, or Facebook's security questions). If user's forgets their password, they can just use familiar recovery tools to recover their login.
Beyond this, the Torus team cannot help you to retrieve your private key, since we can't get access to your 3rd-party OAuth accounts.
This also means that if your 3rd-party OAuth account is hacked, the hacker can gain access to your account. Please follow best practices by protecting your logins with 2FA (eg. Google 2FA).