FYI..I found this in the Database Firewall Installation Guide for version 5.0:
In the unlikely event that an Oracle Database Firewall should fail, all traffic passes through, ensuring service continuity.
However, I have not found anything in the current Database Vault and Firewall 12c documentation that spells this out.
It is really disappointing to see such lack of info regarding such an important aspect that might affect business continuity. if the fail open NIC would do the job why it was not explained well and sufficiently in the relevant AVDF 12c Documentation !!?
I will also update here and share if I got some answers.
Still waiting hopefully on useful feedback here by either Oracle guys or people who has done it.