That's really a bummer. In 2010, before "Michael" came out, there were rumors that Michael recorded vocals for one of the songs without Ne-Yo knowing, i.e., he took one of the submitted songs and started working on it on his own, without Ne-Yo's input. As was the case with Dr. Freeze (APWNN) and Teddy Riley (BOTDF) who submitted song ideas over the years, only for Michael to finish them on his own.
I guess it's not very likely to be true. But I'd still love to hear all six. Ne-Yo was at his peak at the time of their collaboration, and Michael supposedly contributed ideas to how the music sounds...