TestDisk does have an Undelete feature.
It might be possible to copy any files you find to another device. If they have the same name (old and new) you wil have to carefully check their timestamps. You will only find out if you actually run TestDisk.
Failing that you could run PhotoRec in the original USB pen. Choose to search only for Excel files (Advanced Options).
Search the whole disk.
Something else that you could try to recover at least some of your work
In the PC where Excel is installed run a search (Windows Search) for Excel backup files.
Run, Search and in the options find and tick any that will let find hidden folders and/or files
The file extension is .xlk
So your search would be for *.xlk
Select all the files you find and copy them to an external device such a clean USB pen.
You can go trhrough the file names, size, time stamps, etc to recover your more important files.
To do that open the backup files one a the time in Excel. Check that everything is correct before saving it.
Excel will probably overwrite the backup or delete it. Try saving to a different medium or saving to more than one place.
Here is a list of links related to EXcel
Microsoft about the AutoRecovery feature
http://support.microsoft.com/kb/289273
http://www.extendoffice.com/documents/e ... files.html
Ten Essential Microsoft Excel 2010 Tips
http://www.pcmag.com/article2/0,2817,2386994,00.asp
Backup File Name Extensions Changed
http://support.microsoft.com/kb/141451
About XLK file
http://filext.com/file-extension/XLK
Be careful not to overwrite any ongoing work.
Best of luck