I think this link should solve your issues:The Greatest Tableau Tip EVER: Exporting CSV made simple!
There's really not much more I can or should add as it's an excellent write up.
You can get the data back, but not the original Excel worksheet. In particular, it will include the results of any joins, data type detection, and the results of the Excel data interpreter. It also doesn't have any information about the parts of your Excel worksheet that weren't brought into Tableau.