Currently, you can accidentally click on the "X" when clicking on a spreadsheet  tab, which is very easy to do, and it instantly is deleted with no warning and no way to get it back.  

This is a serious problem for me, as I don't know of a workaround.  Suggestions:

1) Add a "Tab Deleted" event so that you can catch this and optionally cancel it.
2) Honor Workbook Protection in Excel so that you could prevent the tabs from being deleted.

Thanks,
Mark