Hi,
While I don't a definitive answer either way, Network cards, to my knowledge, tend to be one of the more reliable components of most server configurations.
This is due, I suspect, mostly due to the lack of moving parts and the relatively static nature of their configuration, hence the focus of Raid systems for HDDs and so forth.
If you are seriously worried about redundency, I'd suggest investing either in the traditional areas of RAID etc. or a complete backup server system.
Regards,
Luke