Worst-case scenario: the UEd Goblin wipes the map and burns down your house.
UTPT or Unreal Tournament Package Tool is a tool by Antonio Cordero Balcázar. It can be used to analyze package files of many Unreal Engine 1 and Unreal Engine 2 games and to export data from them. Unfortunately its latest version, 2.0 beta 5, is from April 2004, so newer games (especially those based on Unreal Engine 3) are not supported.
UTPT can list all objects contained in a package. It can display textures and (static)meshes, play sounds and display UnrealScript source code. UTPT can even decompile UnrealScript bytecode to readable (though usually not compilable) source code. Note that this feature has a few bugs for Unreal Engine 2 bytecode and also never exports subobjects.
Another very powerful feature is UTPT's raw analysis view, where it displays the raw byte data of an object and either auto-formats the data or allows the user to format it manually. This is useful when exporting heightmaps, which is not directly supported in UTPT as it doesn't support 16 bit grayscale textures.