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Does their weapon as of now, deny invul saves? Just automatically killing a unit, thats it?
No. A to-wound roll of 6 against infantry means that the model (if it is multiwound) is sucked into the warp. They can still take an invulnerable save, but it means that 'we'll be back' and 'bionics' and other stuff wouldn't work, because the model is removed from play - fluffwise the weapon /was/ designed to kill necrons.
I would imagine that any upgrades in the new codex would be to ignore invul (like warscythes) on the 6 roll.