IMPORTANT
Until you test another map the editor will keep a backup of the last tested map as WorldEditTestMap located in your maps folder. Example path "C:\Program Files (x86)\Warcraft III\Maps\Test". This file is usually fully editable however it will be overwritten next time you test a map.
If you use JNGP then the JNGP editor keeps a large number of backups in its installation directory. These are generated every time you save a map with the oldest backup being deleted once a certain backup quantity is reached.
Do note that your OS might have baked up some version of the map automatically depending on its settings. In Windows 7 this is done by the "previous version" functionality available when you right click a folder or file. It will only be available if you have configured your System Protection settings to protect the drive the map was stored on and do so reasonably often.
There are common causes for a map to fatal the editor on load.
1. Invalid/damaged import file. Assets such as models and textures are notorious of causing this, especially if used on the map itself (eg a pre-placed unit) so the asset is immediately loaded with the map. When the asset tries to be loaded the editor fatals due to a lack of robustness.
The solution in this case is to remove the imported assets from the map archive. This is done by using a third party MPQ editor like MPQEdit to open the map file (it is a mpq archive) and then remove the imported files from it that are causing the problem. If you are not sure, remove all inputs as you can always re-import them later. Without the imported files the map should then load again. Do remember to make a back-up before editing the archive in-case of a mistake.
2. The map did not completely save. If the editor is force closed during saving or crashes mid-save then it will fail to generate/write some of the map archive files. In this case much of your map may be permanently gone.
You can still use a third party MPQ editor such as MPQEdit to extract whatever files were written. These files can be anything from almost the entire map minus an object editor data type to nothing but imports. Recovered files can be imported into a fresh working map using the third party mpq editor tool so that the missing or damaged files are replaced with blank working ones.
3. The map archive did not write properly or has been damaged. Specifically if key sections of the archive are damaged such as the header, block table or hashtable. Since the archive itself is damaged this is the worst kind of error and it has a high probability that no data will be recoverable.
Depending on the degree of damage some third party MPQ editors might be able to recover some data. However in most cases the archive is beyond use so trying to extract anything from it is impossible. Almost full data recovery could still be possible (if only the archive itself is damaged) with advanced custom written processing of the archive file (similar to how forensic teams can still recover "permanently" deleted data) however it is not viable as the amount of time to recover any data would probably far exceed the time needed to make a new and better map from scratch.
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