If a planes walker takes damage from a creature with death touch is the planeswalker killed no matter what?
It is not. Deathtouch only affects creatures in that way:
702.2b (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=702.2b): Any nonzero amount of combat damage assigned to a creature by a source with deathtouch is considered to be lethal damage, regardless of that creature's toughness. See rules 510.1c-d.