I think some libertarian ideas would be the way to go in such a world. Divvy up the land into plots, where every meter of the land is owned by someone, or everyone (ie: the government). Then allow players the ability to police their land, or build on it, or do whatever they want with it. The 'government' could be little more than the most powerful faction making, and enforcing, laws.
I'm thinking a world like this would work best with something like 50 players. More than that and you suffer the problem of anonymity. Less than that and you lack the necessary people for any sort of organized society.
edit:
Also, the world is never really 100% 'destroyed'. If you destroy the ecosystem, and all plant and animal life dies, you end up playing a kind of post-apocalypse Mad Max game.
:burnup:
