There are no explicit commands to back up only a web server configuration. Simply zip the web server installation directory. After failure, unzip the saved backup on a new machine with the same network identity. If the new machine has a different IP address, update the DNS server or the routers.
This assumes that the web server is either reinstalled or restored from an image first.
The load balancer plugin (plugins directory) and configurations are in the web server installation directory, typically /opt/SUNWwbsvr. The web-install/web-instance/config directory contains the loadbalancer.xml file.