And how many of us (being honest) wish we could have done that after doing
something very silly to a valuable file
Maybe you saved it somewhere you hadn't realised you'd done. Try a wildcard
search from windows.
Start|Search and do an all files and folders search for *.xls
Can you locate it in 'Recent Files' either in Windows or Excel
If all of that fails use your Backup. You do have a backup don't you?