How do I narrate this?

In my one shot, I plan to kill of an NPC that's guiding the party. A monstrous creature will impale her with its leg and attempt to eat her but the party will either prevent it from happening or they fail and she gets eaten( the easy way). If they prevent her from getting eaten by scaring the creature away etc. How do I narrate her death to a party that might use revivify or healing spells on her. Her death is narratively driven

What’s the creature that’s going to kill her? Many different monsters have abilities that render a Revivify ineffective, like Mindflayers, Nightwalkers & Intellect Devourerers.

The best way to narrate her death without these monsters is to just brutalise her body. If the monster kills her, it could easily tear her head off, bisect her or simply ruin her body to such a degree that bringing her back to life would just kill her.

Quote from Punisher_98 >>

In my one shot, I plan to kill of an NPC that's guiding the party. A monstrous creature will impale her with its leg and attempt to eat her but the party will either prevent it from happening or they fail and she gets eaten( the easy way). If they prevent her from getting eaten by scaring the creature away etc. How do I narrate her death to a party that might use revivify or healing spells on her. Her death is narratively driven

I mean if the monster is supernatural enough it could eat her soul as well. Imo, it feels more threatening to have monstrous creature devour the being of someone instead of just turning them into a snack. Maybe it has some necromatic magic  running through its blood, letting it heal itself and wither others? Idk just some ideas

Eg narration : "The monstrosity glares at her as she lies helpless on the ground, stabbed from its powerful talons.  In one swift motion, it uses its claws to pick her up, and it bites her head of. As you all watch in horror, you swear you hear the sound of her soul shattering into a thousand pieces from the sheer, necrotic energy that this monster possesses. It turns its head to look you dead in the eyes, with no soul behind the terrifying gaze it possesses"

Quote from ClassicCharismaCaster >>

The best way to narrate her death without these monsters is to just brutalise her body. If the monster kills her, it could easily tear her head off, bisect her or simply ruin her body to such a degree that bringing her back to life would just kill her.

This was going to be my suggestion as well. Depending on graphic your party wants violence, you can describe how the body has already been mutilated in such a way that it just cannot be revived. A few vital organs lying around in the grass and some limbs up in a tree or sunk in a lake, etc.

And one option is to just narrate it through as a "cut-scene". Maybe have them make a roll for something their character does and just describe how whatever-it-is-they-rolled isn't quite enough (even a nat 20 doesn't have to mean auto-success).

One key thing with all the reviving/resurrecting spells is that the soul has to be willing.

If she gets eaten, then the corpse is chewed up so no going back there.

If the party saves her, when one of them tries to heal her, have her lay a hand on theirs and say "It's ok; I'm ready.". Then she dies, and she doesn't come back.

If she's already dead, then offer the healer a brief vision of her, with a corridor leading to >insert white light, beautiful gardens, or the gates of hell accordingly here<, where she tells them that she thanks them for the effort, hands them back the diamond, and tells them that she does not wish to return to life. You may be able to use this as a moment for the plot - either she tells them something important, or she says something like "I'm not supposed to tell you more, but the treasure is in the abandoned..." as it fades out to whiteness, leaving them to guess at what the whole piece of information would have been.

I'll be a contrarian voice here: Is it necessary that the PC's be unable to revive or heal her? If they save her life, does it screw up some plans later on? If the answer is 'no,' then I would let the choice of whether to save her be left to the PC's. The players know very well the resources they have, and that spending a resource now means it won't be available later.

Quote from Stabbey_TC >>

I'll be a contrarian voice here: Is it necessary that the PC's be unable to revive or heal her? If they save her life, does it screw up some plans later on? If the answer is 'no,' then I would let the choice of whether to save her be left to the PC's. The players know very well the resources they have, and that spending a resource now means it won't be available later.

 Also, if your plan requires the character to die, but the players have ways to prevent that, it's not a good plan. Either do it off-stage, so they can't stop it, or accept the possibility that the character won't die.

(Also, be prepared for the players to not react how you think they will. I've killed off an NPC at the very start of a campaign, in order to give the players agency, and had the players immediately make reviving the NPC their goal.)

Don't worry about the player's response, that's their business. Don't bank too hard on the players reacting one way or the other, you should make sure the plot has room for player choice. 

Either the monster eats the NPC or it doesn't. Either way, there's a way.

If the monster eats the NPC: Revivify is a touch spell. You can't touch someone who is inside a monster's stomach.

If the monster fails to eat the NPC: Revivify gives you the ability to restore life to someone, but what if the target doesn't want to come back? Simply rule that the spirit must be willing to return, and this one isn't. Narrate that the cleric presses the diamond to the NPC's chest and says the required prayer. But instead of the diamond shattering and the NPC waking up, the cleric sees a vision in their mind of the NPC telling the cleric that they have guided the party far enough and that the party can find their way without the NPC now. And since the spell didn't function, the diamond is not expended.

Healers often have a "No one left behind!" mentality, so when a death is preordained, you have to give them a cut scene to show that it's okay to let them go. 

If the players choices don't matter - the NPC is dead either way - don't pretend that it does matter. Make the NPC's death super obvious otherwise the players will be annoyed if they can't save them. So I'd go for something like the monster crushing / destroying the NPC's head so it is abundantly clear Revivify isn't going to work. Alternatively, have some demon appear and claim the soul of the NPC - note that only use this if you are ok with the party going on a whole side-quest to try to save the NPC's soul from Hell or wherever. 

If the body is savaged by the monster, she can't come back. If it isn't, and the players can revive her, the party probably will. If you really need the NPC to die, then just tell the players the body is too far gone and her soul doesn't want to come back-that's that. If you don't care either way, then give them a chance to. It all hinges on exactly what you want to happen to this NPC.