Save the current version as a new name.
Open the old version (you still have that, right)??
Copy the worksheek from the old version to the new version.
If you had formulas in other sheets that pointed to the "deleted" sheet, you'll
have to fix those.
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If you haven't saved after you've deleted the sheet:
Lots of times, it's just easier to close without saving (losing all the changes
you've made since your last save). Then reopen a good copy and make all those
changes again.