FWIW, that seems as legitimate to me as relying on a Revivify spell. The tactic could still go wrong in a number of ways: (1) Hostage's HPs are low enough that the villain insta-kills the hostage with no death saves required; (2) villain knows the gameworld physics as well as you do and is planning on sawing the victim's head off (i.e. stabbing for auto-crits until 3 death saves are achieved); (3) there may be repercussions for getting your throat cut and surviving it, e.g. it may be very painful and cause psychic trauama or leave scars.
The PCs are probably
aware of all these factors, but the reality of the universe they live in is that for some reason, people
don't die as easily as they do in our universe--so it would be wrong to transpose attitudes from our universe into that one.
Amputation of limbs is very difficult under the 5E ruleset (I allow if only if you've already failed one death save and therefore your spirit is starting to dissociate from your body), so NPCs at my table look on amputees with a special horror that a medieval peasant from our world would have trouble relating to. Captain Hook isn't just odd to these people, he's disturbingly
wrong--as wrong as mating a grizzly bear to a giant owl.
I don't get the feeling that we
are quite on the same page, because I don't get the feeling that you would extrapolate the world this way. Maybe it's partly because I come to (A)D&D from a Spelljammer background; binary gravity and phlogiston and alternate physics is part of what D&D is and always has been to me. People in my 5E game aren't even made out of atoms, they're made out of vaguely Aristotelian elements like "flesh" and "bone".
(What I don't get about the death saves/hostage scenario is why any DM would set up those rules for his game and then get upset when the PCs want to play by them. Or rather, I understand it at an intellectual level--those DMs probably see the rules as loosely modelling the game world, but the master copy of the world is the fiction in the DM's head and not embedded in the rules--but I don't relate to it emotionally. How could you blame players for playing by the rules you gave them for the universe you invented? I can understand a DM feeling dissatisfied afterward and wanting to revise his rules because it didn't match his intended aesthetic, but I can't understand why he would be upset at the players and not at himself.)
They were playing by standard 5e rules. The players didn't know that NPCs wouldn't have death saves, or that excessive damage could kill them, etc, and neither did the new DM.
I would have no issue whatsoever with your Spelljammer campaign. You've specifically decided on an alternate physics for your campaign. I'm just saying the physics in your campaign should function the way you want them to, and not be changed inadvertently because of the way the rules are written. I do agree with you. If you want the physics of the world to mean that rocks are springy and falling doesn't cause damage, that water is toxic to orcs, and people don't need air to breathe, or whatever else you come up with, it makes no difference to me. It's your world. But the rules (likely after some modifications by you) should support that, not change it.
The death save rule is not put in place to change the physics of the default campaign world. It's there to make the PCs a little more resilient so they don't die so easily. Resurrection magic is more readily available, also so players don't have to lose their PC if they happen to be killed. If a DM wants to make that into a world where people actually view resurrection magic as common and failsafe enough that people don't fear death, and where the death saves actually have a recognized and expected effect, then fine. People don't fear death like they do here, and folks might actually know somebody who has been revived or resurrected. But I don't think that's the intention of those rules - they weren't making a world-building decision, they were making a decision to prevent players from being upset if their favorite character died.
But the DM clearly wasn't doing that. He was doing a classic hostage situation, where threatening the life of the hostage sets up a dilemma for the PCs. In the DMs mind the physics of death were the same as they are here. Permanent, and that cutting the throat of somebody is pretty much a guaranteed death.
The players (wrong) interpretation of the rules led them to view the physics of the world through the lens of game rules, rather than the fictional world. If it were a PC, then they would have received the death saves anyway, in which case their interpretation of the rules would have been correct, and I still think it's the wrong solution for the PCs to come to unless the physics of the world have been specifically defined in a way that death works differently.
I have no problem with amputation or decapitations in my campaign. It's not easy to do, but it can happen and I have the rules in place to support it. It's another good example of how the rules can change the actions or physics of the game. The Angry GM had a session where his players fought a hydra, and not one of them tried to lop off a head. He asked why afterwards, and their answer was that they didn't know they could do that. There's actually a relevant rule, but it's in the description of the Hydra, and his players hadn't read the MM. They were of the mindset that if the rules didn't say you could do something, then it wasn't allowed.
My point is really that the world and its physics should work the way you want it to, and not be changed because of a game rule.
