I restarted my MacBook Pro today and my HFS+ partition decided to disappear. I wasn’t able to boot OS X any more and Disk Utility in Recovery Mode showed the space as empty.
So installed OS X to an external media and booted from that.
Started Disk Drill on the fresh OS X install and lucky for me, it found the ‘Macintosh HD’ partition. I clicked the Rebuild button and waited for the catalog file to be rebuilt.
After the rebuild, I saw all the files I had on the partition and continued by pressing ‘Rebuild’ and then ‘Confirm and rebuild’.
After the Rebuild was done, I clicked ‘Finish’. After this, I was hoping to see my missing partition under Finder, but there was nothing new there. I also checked from Disk Utility and it was still telling me I had almost 400 GB of ‘free space’ on the drive.