SimCity to SimJungle (and back?)

Unsurprisingly, SimCity focuses on the economic and social aspects of a successful city. Not enough money and people become unemployed and leave, not enough electricity or transport and various undesirable consequences follow. When people do leave and industries shut down, the result is rather boring bits of wasteland and delapidated buildings.
In reality, this isn't all that happens when a city is abandoned, cases in point including the Mayan cities and Chernobyl. In actual fact, "nature" takes over. I think this should happen in a city simulation game.
The game has two modes, each of which includes features of the other. You start off with an empty piece of land with a certain climate, terrain, water and local flora and fauna. You manage this piece of land both ecologically and economically, so either a city or a rural ecosystem can develop. If something happens to the city, for example the nuclear power plant melts down, it becomes abandoned due to economic failure or there's a natural disaster of some kind, the city fails in human terms, but not in ecological terms. Although the human population abandons the city, the likes of rats, cockroaches and stray dogs increase in population and plants in the "waste ground" begin to progress towards whatever the climax community is in the locality. Forest may take over, leading to a "lost city", or wetlands may emerge with herons, otters, beavers and fish. At the same time, human beings may still be in the picture, perhaps leading a nomadic lifestyle, settling in small villages or following the Mad Max dream. The precise details of what happens depend on the historical period and location of the initial piece of ground. It's also important to manage the ecology of the city as an urban environment, so for instance poorly-managed sewers or a stray pet problem can become an issue.
Extra natural disasters are available, such as plague, volcanic eruption, ice ages and so on. I also imagine the music changing tone, so for example it becomes classical and pastoral in a temperate region, thrash-metally in the Mad Max scenario or characterised by a succession of repetitive beats in a rainforest region. Hard to pull this last bit off without stereotyping though.