Signals Notebook: Can we have a user account who can use Signals Authentication in case SSO/SAML fails

No, there is no such provision. 

Instead, organizations can request for an alternate domain pointing to the same tenant which uses Signals Authentication. 

E.g.:

https://xxxx.signalsresearch.revvitycloud.eu/ ----> SSO 

https://xxxx-yy.signalsresearch.revvitycloud.eu/ ----> Signals Authentication

So, if by any chance SAML Authentication fails, there would be two options:

• Login using the alternate domain - https://xxxx-yy.signalsresearch.revvitycloud.eu/ and correct the SAML configuration.
• Contact Support in order to revert the affected domain to Signals Notebook Authentication.