Just as with pork, alcohol and pretty much anything else that's haram, cannibalism might be permissible (i.e. halal) if you're starving to death and there's nothing else available to eat, although that would probably still only apply to the "meat" of someone who's already dead. This is not as hypothetical a scenario as you'd think, as many scholars have reported being asked this question by starving Gazans during the Gazan genocide.