They will have to prove that he was, in effect, blameless. And let's assume he was, I think that might be rather hard to prove.
No problem. Just overcome the concepts of:
1. Required flight-deck crewmember.
2. CRM
3. Second-in-command.
4. The concept of weather minimums and the regulations against violating them in commercial operations.
You get by those, he gets off as a passenger.