Make a redirect if NAT out interface is down

Hello,
I have a question about possibility of making a redirect if NAT out interface tun0 is down. This is iptables rule for Masquerading our network via VPN connection.

iptables --table nat --append POSTROUTING --out-interface tun0 -j MASQUERADE -m comment --comment "Masquerading"

When VPN goes down, we can't access some resources and we need to verify its status and establish it again. Is it possible to make a redirect of all traffic to another host - Web Site(via IP address) of tun0 is down ? In this case all users immediately be seen that VPN should be established.

Thanks.

Sorry for my English.