Can a Zealot Barbarian at 0 hp be disintegrated?

Question

A Zealot Barbarian gets the feature Rage beyond Death at Level 14 which reads

Beginning at 14th level, the divine power that fuels your rage allows you to shrug off fatal blows. While you’re raging, having 0 hit points doesn’t knock you unconscious. You still must make death saving throws, and you suffer the normal effects of taking damage while at 0 hit points. However, if you would die due to failing death saving throws, you don’t die until your rage ends, and you die then only if you still have 0 hit points.

My question is, if a Zealot Barbarian is already a 0 hit points and gets hit by a Disintegrate Spell, does it turn him to dust? Since the Disintegrate spell reads

A creature targeted by this spell must make a Dexterity saving throw. On a failed save, the target takes 10d6+40 force damage. If this damage reduces the target to 0 hit points, it is disintegrated.

Since the Barbarian is already a 0 hit points his hit points aren't being reduced to 0 hit points. Does that mean the Spell won't disintegrate the Barbarian or is my reading of the Spell incorrect?

Answer 1

RAW: the barbarian will be disintegrated

The rules now say this explictly per the 2018 PHB errata to close what was previously a loophole.

The target is disintegrated if this damage leaves it with 0 hit points.

Since, the barbarian would be at 0 HP after taking the disintegrate damage they would be disintegrated.

The loophole was never intended

Jeremy Crawford, lead rules designer for 5e, confirms this loophole while also confirming that it was unintentional in this tweet (made before the 2018 errata):

The disintegrate spell has a loophole in it. RAI: The spell disintegrates you whether it deals damage to you when you're at 0 hit points or it reduces you to 0 hit points. RAW: You aren't disintegrated if the spell deals damage to you when you're already at 0 hit points.

Answer 2

As of the November 2018 PHB Errata, the Barbarian Dies

The new wording from the errata is as follows:

“The target is disintegrated if this damage leaves it with 0 hit points.”

My original answer will remain below, despite being disputed by other answers as well as by Crawford.

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Yes

In the rules for taking damage it says:

When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum...

The book consistently refers to damage reducing to 0, even when it surpasses current HP. We know that being reduced from 1 HP to -1 is being reduced to 0. Logically that means all HP below 0 is equal to 0.

Therefore, effects that trigger when a target is reduced to 0 hit points should trigger any time that it reduces them past 0 hit points.

If this wasn't true, that would mean any unconscious person would be immune to the disintegrate aspect of the spell. It makes no sense that because you are already at 0 HP you become able to resist spell effects like this, and the Zealot Barbarian offers no specific override for this, therefor the special effect applies.

In a related matter, here is the relevant Sage Advice pertaining to disintegrate vs Wild Shape, Half-Orc racials and the definition of "Dying Outright".

Answer 3

No, a zealot barbarian's lv 14 feature Rage Beyond Death does not protect it from disintegration. However, the barbarian's lv 11 feature, Relentless Rage, can prevent its HP from dropping to 0, which does prevent the barbarian from being disintegrated as long as it continues to pass a constitution saving throw to instead be conscious with 1 HP.