Q. Is there a way to mention one more server as standby authentication server which can handle authentication requests in case the primary fails?
A. Yes, just specify the new server with your aaa-server commands, but it will only go to the second server if the primary doesnt respond. If the primary does respond, as if its denied, it wont go to the seconday.
Q. Also can i mention a local username and password which myself as an administrator could use for authentication in case the firewall is not able to contact the Radius server?
A. Sorry, can't do this yet, not for VPN anyhow.
KD