The original backdrop used in AmiKit 1.2.0 is located in AmiKit:Prefs/Presets/AmiKit/Backdrops/1152x864/ folder. It has never moved, it's the Magellan's configuration that has been changed only. Similarly, if you were using another backdrop, you can still find it in the same location, just change the Magellan's settings according to FAQ:
Hold down the right-mouse button over the picture file and select "Set as Background". Use the Directory Opus Environment Settings (right mouse -> "Settings" -> "Enviroment...") to save your new settings.