I just updated the wiki to include some new playback commands. That command is still there. Thanks.
That's rather puzzling, as I ran a search on that page for 10078 before making my post. However, that command is certainly there now and I've now given it a try in a BAT file triggered indirectly by a link in PowerPoint.
MCC_CLOSE_PROGRAM_AFTER_STOP = 1 doesn't work in Standard View, but if I specify MC33.exe /Mode Mini and play audio files it works well enough for my purposes. I have Mini View configured to be 'Always on top'. In those circumstances, MC simply remains in the foreground in a faded version without ever having the focus while the music is playing. Despite the name of that command, MC never actually closes.
That MCC command has no effect at all when I play video files (which obviously require MC to have the focus during playback). Is there any chance that the command could be modified to work as advertised and close MC, in which case I'm guessing it would handle video as well as audio?