I think since the parts are already targetted that each part should have a HP value. If the head takes 200 hp and the character only has 218 HP, this character should be dead as there is no way a head can have the majority of the HP total. And if a hand takes 200 HP in the same example above, it should be useless, ie. -1 attack per round.
This is probably the intention anyway, to be implemented soon(tm) of course.