The system backup of GAiA should also be accompanied with a backup of the Clish configuration file in GAiA. But when disaster strikes and all you have to go about is the system backup file, you can find the interface IPs and route information in the .tgz-file

After extracting the backup file (tar -zxvf backup.tgz) you can find the following information here:

ifconfig

The IP addresses of the firewall can be found in ./tmp/backupinfo. The first bit is a copy of the ifconfig-command output.

Routes

The routes configuration can be found using the command cat ./config/db/initial | grep static which will display something along these lines:

routed:instance:default:static t
routed:instance:default:static:default t
routed:instance:default:static:default:gateway t
routed:instance:default:static:default:gateway:address:10.20.255.1 t
routed:instance:default:static:default:gateway:address:10.20.255.1:preference 1

Hope this information comes in handy for someone.