Minecraft is a game, it is a game involving blocks, withers and endermen, zombies and creepers. Many people will have made a house or even a city, but how long will it take for endless seasons of mobs to spawn in the houses? We shall see, $^$&*^%^&*$^%* yeh!
1 day after admins:
The city will still look the same, griefers may have griefed some of the houses and raided chests while leaving the players annoyed, mods like tekkit could have shut down inventions and explosives like TNT or nukes gone off for no reason ( maybe something else to do with the inventions or whatever ).
1 month after admins:
The city is now looks like a giant hole in the ground beacause of tnt griefers, the owners are very annoyed while most of the torches have burnt out by now, not many supplies are left to do with both raiders in chests and the fresh supplies on griefers or n00bs, the players can't do much about the tourchs unless they find another fresh city but now mobs have started to spawn.
1 year after admins:
By now the city has no supplies left and is bunch of floating blocks. All the good supplies will now be gone like iron blocks or diamonds and obsidian, massive ammounts of mobs have spawned and creepers blow up the remains.
Then the admin comes back and resets the sever.