Is the portion you deleted perhaps saved in your clipboard?
Open up Excel and select the whole worksheet in a new document and select Paste. Perhaps your data is on the clipboard.
the only other possibility that I know right now, and time is of the essence, would be to go to your TMP folder and see if a large file is there about the same time you remember deleting/changing the data. Perhaps you got an auto TMP save.
change the tmp file to an .xls extension and check.