I am relatively new to Tableau and may have encountered some data loss .. but let us proceed to see if there might be some means to salvage the data.
Upon re-loading a workbook after a couple of weeks of non use we can see reference to an Extract load attempt from a temporary (OS/X) location:
Now I had not realized that the Extract was not being saved with the .twb itself - and even less that it was in a transient disk location.
So .. is the data gone? Secondarily - did I miss some step that would nudge me to save the extract to a non-volatile/non-temporary location on disk?