Temp HP, and abilities that reduce you to zero HP

The title says it all: Does the temp HP go away? Does it stay? Would it keep them alive?

If you still don't understand, this is taking about getting set to zero HP without damage

According to the rules on Damage and Healing in chapter 1 of the Player's Handbook, temp HP don't count as healing and do not restore you to consciousness if you're at 0 HP.

I was asking: What happens to the temp HP

Quote from Tana___ >>

I was asking: What happens to the temp HP

Nothing. But they don't really do much while you're at 0 HP, so it's rarely going to matter.

Temp HP get depleted first, so it would be unusual for a scenario to happen where you went to 0 normal HP but still have Temp HP.

I think the OP means something like power word kill, fewer than 100 hp and you die, but what if you had, say 99 hp and 2 thp. Does that put you at 101 so you’re not insta-dead or 99 do you are?

I'd rule "no"; temp HP is a separate buffer from regular HP, and gaining temp HP isn't healing.

There are not a lot of abilities that just reduce hp to 0 without doing damage, and several of those have hit point thresholds. I'm inclined to say temp HP are lost but also count towards the HP threshold.

Quote from Tana___ >>

I was asking: What happens to the temp HP

 If the affect doesn't deal damage, nothing.  But if you're reduced to 0 HP, that typically won't matter much.

According to the rules, I don't see why your Temporary Hit Points would disappear if a game feature reduces you to 0 HP, and they wouldn't stop you from falling Unconscious:

When a creature drops to 0 Hit Points, it either dies outright or falls unconscious, as explained below.

Temporary Hit Points last until they’re depleted or you finish a Long Rest (see the Rules Glossary)

Given that being reduced to 0 by effects such as PWK neither deplete temporary hit points nor trigger a long rest, the temporary hit points would persist.

Quote from Xalthu >>

I think the OP means something like power word kill, fewer than 100 hp and you die, but what if you had, say 99 hp and 2 thp. Does that put you at 101 so you’re not insta-dead or 99 do you are?

Well, let's think about the design purpose of THP. They seem to be intended to serve as a buffer to your hit points so that you're a little harder to kill. They're also called temporary Hit Points and not anything else. For that scenario, my ruling would be that the THP puts you at 101 and therefore you would not instantly die.

Hit Points and Temporary Hit Points are distinct and different, to the point that they get a specific call out to that effect:

They’re Not Hit Points or Healing

Temporary Hit Points can’t be added to your Hit Points, healing can’t restore them, and receiving Temporary Hit Points doesn’t count as healing. Because Temporary Hit Points aren’t Hit Points, a creature can be at full Hit Points and receive Temporary Hit Points.

If you have 0 Hit Points, receiving Temporary Hit Points doesn’t restore you to consciousness. Only true healing can save you.

As such, a feature such as Power Word Kill that explicitly states Hit Points is not referring to Temporary Hit Points.

Your Temporary Hit Points shouldn't be depleted if you die outright or you're otherwise reduced to 0 Hit Points.

Quote from Plaguescarred >>

Your Temporary Hit Points shouldn't be depleted if you die outright or you're otherwise reduced to 0 Hit Points.

Which leads to the (perhaps a bit odd, but I think technically correct under the rules) situation where a dead body could still have temporary hit points, which I guess it would retain if resurrected.

Yes, but typically only Revivification would be fast enough for those temp HP to matter.

Quote from wagnarokkr >>

Quote from Plaguescarred >>

Your Temporary Hit Points shouldn't be depleted if you die outright or you're otherwise reduced to 0 Hit Points.

Which leads to the (perhaps a bit odd, but I think technically correct under the rules) situation where a dead body could still have temporary hit points, which I guess it would retain if resurrected.

  I agree it would be odd case.

Quote from 6thLyranGuard >>

Yes, but typically only Revivification would be fast enough for those temp HP to matter.

Well, I don't know, it depends on where you got the temp HP.

In a lot of cases they don't go away until you take a Long Rest, and you can't take a Long Rest if you're dead (you specifically have to have at least 1 real HP to start one).

Question: If you have Temp HP while at 0 HP, and you take damage, would you suffer failed saving throws?

Damage at 0 Hit Points. If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death.

As you would be unconscious, all attacks that hit would be critical hits, and you would suffer two failures. 

But lets say you have 0HP, and 15 Temp HP. A goblin hits you and does 12 total damage on the Critical Hit. Would the Temp HP buffer you from failing two death saves? RAW it seems like not, but I'm curious to hear people's perspectives. 

For reference: 

Temporary Hit Points

Some spells and other effects confer Temporary Hit Points, which are a buffer against losing actual Hit Points, as explained below.

Lose Temporary Hit Points First

If you have Temporary Hit Points and take damage, those points are lost first, and any leftover damage carries over to your Hit Points. For example, if you have 5 Temporary Hit Points and take 7 damage, you lose those points and then lose 2 Hit Points.

Temp HP does still say you "take damage".

Quote from MaximusArael020 >>

Question: If you have Temp HP while at 0 HP, and you take damage, would you suffer failed saving throws?

As far as I can tell from RAW, yes (much like damage to temp hp can still trigger concentration checks), but the temp HP will help prevent death from massive damage.