Well first off there needs to be a reason for the carrier's destruction, and that usually means somebody shot it down. Maybe there could be a few locations scattered around the world with Really Big Guns a la Subnautica, that you have to shut down somehow or destroy? That way you can easily justify the no air vehicles rule, and give the players some clear objectives to complete in order to 'win' the scenario and escape the planet.

To be perfectly honest though, I'd be utterly content roving around in a souped-up dump truck, blasting away at enemy bases and carving out my own little empire of scrap.

I think it would be cool to have multiple factions on the planet, some that you can befriend and use economy features to trade with.