Unfortunately you have saved .twb instead of .twbx.
Always save Tableau Packaged workbook which will store embedded data on the same for you.
in .twb there is no embedded data so in this case open your workbook even after error if you can and try to connect to the data source one more time.
The workbook you posted has no xml data. All I see NUL for the xml structure. I believe your workbook was corrupted some how . The log files, Documents -> My Repository -> Logs -> logs.txt , might hold a clue to what happened. I would reach out to Tableau support. They may or may not be able to help you.