Remove partition failed - the partition is gone, but now there is missing space. How do I get it back?
Backup your main volume.
Open Terminal.app
Check the file system integrity of your main partition: diskutil verifyVolume disk0s2
If everything is fine, expand your logical volume group (and the inherent logical volume):

diskutil cs resizeStack lvUUID size


In your case that's:

diskutil cs resizeStack 8679E121-03C8-47B0-844E-961A437E5CA5 0g


If you run Sierra the magic size 0g may fail and you have to enter a distinctive size:

diskutil cs resizeStack 8679E121-03C8-47B0-844E-961A437E5CA5 999300m


If you get an error like: Error: -69771: The target disk is too small for this operation choose a slightly smaller size like 999200m until you are successful.
If you get a different type of error, the whole (previous) Disk Utility operation failed and corrupted the internal structure of the LVG. You have to restore the main volume from your Time Machine backup then.