How much do you think an ability that allowed an artifact weapon to bypass the Cosmic String property of its target, no matter how weak the wielder is in Immortal terms, would cost, in terms of weapon bonus? That is, if this weapon kills the target, then that target is dead Dead
Dead, not coming back or in an inactive state as would be normal for Cosmic String.
I'm sort of assuming the weapon would be able to bypass up to the level its actual creator is at, so a weapon like this created by an Elder One would only be able to kill Elder Ones- but the question stands as written.