In Tableau version 10.0 onwards, you can recover older/previously changed workbook versions, but only if the workbook exists in the project folder.
It's an option in Tableau Online. Please see this post: Restore your workbook with one click in Tableau 10 | Tableau Software
However, if it is actually deleted, then the version is likely not there, unless perhaps you accidentally overwrote it? If that's the case, then the above might work for you.
If you're publishing from Tableau Server then there's the possibility that it exists in a backup, if the server is being backed up.
If you need to know what actually happened on Tableau Online: (1) Go to Status (2) Select Actions by Specific User (3) Filter to action (deleted workbook) to see what actually occurred.