I think most of people have the following experience: Sometime somebody will delete some useful files by miss in Flex builder. When it happened how disappionted you are and maybe several weeks efforts was disappeared. In fact these deleted files could be restored in Eclipse. Since Flex builder is based on Eclipse, the way could also be used.
To restore a file from local history, right click on a folder or a project in the Navigation view, and from the context menu, select “Restore from Local History…”
More detail please see here: