John Legend recently stated (in the Smooth Radio Interview) that Michael Jackson asked from him to write (with the help of will.i.am) some musical ideas for his upcoming studio album at that time.
For example, there is a specific track with a late '70s - mid '80s feel to it, but apparently the song has only music on it (as John Legend revealed, there is a little David Bowie energy in the track with the guitar part).
John Legend did not categorically state that Michael Jackson recorded (vocally) any of these songs, which strongly implies that all of them remained in the form of musical ideas only.