If you're the owner of a deleted sheet, you have up to 30 days to recover it; after that the sheet will be permanently deleted.
Workspaces and folders cannot be recovered—you'll need to rebuild them.
To recover a deleted item:
On the left Navigation Bar, click Browse.
Scroll to the bottom of the Browse panel and then click Deleted Items.
Right-click the item and select Undelete. Recovered items move back into your Sheets folder.
You can also drag the item out of the Deleted Items section and drop it in a folder or workspace to undelete it.