Many nova-networks....There's my reason

I'm thinking about HA recently..

Nova-network is the most one which I want to do HA.

http://1.bp.blogspot.com/-DU2OzGt8QTw/Tb6MtEdLGWI/AAAAAAAACm0/Ow3HlghvFaM/s1600/mult1.png
In this topology.....
Due to instance's gateway from nova-network host, once it dead , might lost all connection of instance .

http://i217.photobucket.com/albums/cc280/tonytkdk/new.png
In this architecture , instance can be access anytime in internal network even nova-network dead. But it can not run up new instance at all.
and I believe that instance can not connect to google any more , bcz instance lost gateway.

1. Is there any approach to make instance routing from another router? In flatDHCP current condition , nova-network must redirect 169.254.169.254 to API server for instance fetching metadata.
Actually , reset routing table manually in instance might work.

2.Or run with multi nova-networks in a Openstack NOVA environment, but I did not figure out any approach yet.
In doc http://nova.openstack.org/devref/zone.html?highlight=zones
I saw a description "Pushed further a Zone may contain many API nodes, many Scheduler, Volume, Network and Compute nodes as well as a cluster of databases and RabbitMQ servers."
many nova-network hosts .......is it possible?

Any suggestion will be great :)