Hi,
it's about the gateway himself (not a client-of-the-gateway). A gateway router (has to/)should check his default route and change his role to 'ordinary-client' => switch working state from -g to -r/-p Mode. May think about NATed LAN-clients, too...
this is quite difficult to implement. The dyngw plugin tries to do exactly the same thing. Various approaches were already tested and they all had their problems. How do you want to find out whether internet is available or not ? Ping, traceroute or dns ? As far as I remember we always had situations where this detection failed. The latest example: Run OLSR with the dyngw plugin on a batman host which is searching for internet (-r). The plugin will find out that internet is available via batman and happily announces a default route in the OLSR network ...
I think the difficult part are the endless scenarios we would have to cover. But if someone has a good idea I certainly will implement it. :-)
Regards, Marek