Decay over time is something I want to do, but that’s further off still 
Basically each tile type would need to have a half-life and a decay product. Any time the map is loaded, it caclculates a probability for each tile, and if it fires, changes the tile to the new thing (moldy wall instead of wall, or vine covered, or crumbling).
The same thing could apply everywhere, weeds growing through asphalt and concrete, underbrush growing thicker, even buildings collapsing.
