I had the same thing happen. After hours of work, the Turbo Tax file is gone. Using Turbo Tax 2019 Deluxe for Windows. I've searched the entire hard drive, the Recycle Bin, and One Drive. I tried calling support and there was nothing they could do. All of my old Turbo Tax files still exist, but there is no .tax2019 file. It wasn't in my Carbonite backup either, so I suppose it is not one of their default file types, or the file was open (I tend to keep Turbo Tax running for days, util I complete the return) and couldn't be backed up.
