You launch a green ray at a target you can see within range. The target can be a creature, a nonmagical object, or a creation of magical force, such as the wall created by Wall of Force.
A creature targeted by this spell makes a Dexterity saving throw. On a failed save, the target takes 10d6 + 40 Force damage. If this damage reduces it to 0 Hit Points, it and everything nonmagical it is wearing and carrying are disintegrated into gray dust. The target can be revived only by a True Resurrection or a Wish spell.
This spell automatically disintegrates a Large or smaller nonmagical object or a creation of magical force. If such a target is Huge or larger, this spell disintegrates a 10-foot-Cube portion of it.
Using a Higher-Level Spell Slot. The damage increases by 3d6 for each spell slot level above 6.
* - (a lodestone and dust)
So on a successful savning throw nothing happens or half damage ?
Doesn't say they take half damage on a successful save, so nothing happens.
I've never been able to accept that the ray is green. In my mind a good disintegration ray should be red or white, never green, especially when finger of death already exists as a zombie and necromancy version of disintegrate that should be green and zombie/necromancy themed.
I would rule that a clump of hair cut off and stored somewhere safe could later be used as a valid source for a druid to cast reincarnate to get around the True Resurrection or Wish limitation. Rules as Written explicitly state that the target can only be revived by Wish and True Resurrection but that's because no body remains to revive. Since Reincarnate only requires a piece of the body (the hair) it should work imo