If you want to give files that have been renamed their old names, you just select them in the filelist and click the Undo-Gadget.

If this function was disabled(Undo active in Prefswindow while the files were renamed, it is not possible to give the files their old names.

Something about datasecurity:
In an animation it's very important to have the right order of frames. It's even more important that this order is not messed up. Therefore, ProRen has the undofeature. But computers may have accidents and crash in the very wrong moment, so I thought about a very safe undo.

Before a file is renamed, it's name is stored as a filenote. It is not necessary to open the file to do this and so the contents of the file are not in danger. If the computer should really crash, the harddisk may have to be validated, but the file is not damaged. Of course I can not guarantee this for any computer and any file and ... but I've tried it on my computer and normally even the filenote of tha last file is intact.