Some folks have taken to applying the {filenamebase} variable to some unused IPTC field during ingest ("Supp Cat 3" as an example). I do that myself with a local IPTC stationary pad during my basic ingest. That way, the original filename as it was during ingest is always available in the event of a renaming mishap.
Also, depending on your camera or what edits you have done, the {frame} variable might also still have the frame number from which you might be able to recover the original filename. For example, renaming the files with "DSC_{frame}" or "IMG{frame}" might get you that original back. Not sure if that would help you or not.
As always, keep in mind that the Rename dialog shows you a preview of what the new filenames will be so that you can make an informed decision about proceeding. :-)
-Mick
