How do you not have players kill your quest giver?

[SangoProduction]

Let's say that your players are the generally reasonable folk, not the murder hobos.

So, I got a hold of this module that seemed really fun. Problem is that the module's main quest giver is the guy who sent the drow after the party, with a letter incriminating itself....as the entire hook for the module! OK. So, clearly evil dude who is telling drow to kill people. Oh, and would you guess he was a demon lord the whole time? Wow. I never would have guessed.

I think I'm going to change that. I've read the first couple of pages, and it seems as though the players are just expected to not question it at all....which is a little insane.

But, let's assume we keep the idea of this demon lord commanding drow as a quest giver. How the hell do you make it so they don't kill him, while maintaining a hint of player agency?

It's Expedition to the Demonweb, I think.

[Rynjin]

Make him speak through some kind of mouthpiece. The variety depends on how sinister you want to go.

Less sinister: A simulacrum. If destroyed, it's no big deal.

More sinister: An innocent bystander; the party can't "kill the quest giver" without killing an innocent person.

Most sinister: Through a PC. Comes in two flavors.
--Suped up Magic Jar or Possession.
--Nightmare

[Geddy2112]

I second mouthpiece or indirect communication. Animal messenger works, but is easily intercepted. If you use a sending spell, it is a surefire way so long as the target is on the same plane of existence. Can't be saved against/no spell resistance, shoots through mind blanks, sleep, etc etc. Limited to 25 words, but you can cast multiples if you need to deliver complex instructions.

[noob]

Maybe make the quest giver try to kill the pcs first?(right now he is a demon lord so for him to kill the pcs and turn them into intelligent undead under his control would not be that hard)
I mean it is a demon lord so either he really wants the adventurers to work for him(in which case turning them in undead can be the most reliable way) or he would not even know he have those adventurers work for him(someone would have done the job for him)

[Necroticplague]

Easy: crank up his stats so that taking him on is suicidal. They’re free to try, but that just lets him kill whichever PC could damage the module’s plot the most to prove his strength before strong-arming then into doing whatever dirty work is needed.

[Darth Ultron]

Well...

1. Let the quest giver die? So what? As long as the players do the quest.
2. Let the players do an attack if they want. As the fight as no real meaning, it's not like the quest giver has any reason to stick around and fight. So they just go away and escape or mop the floor with the players.
3.Have the quest giver be an illusion, clone, shapeshifter or whatever...not like the demon lord does every little thing.
4. If the quest is ''worth it'', the evil quest giver can play the ''ok, I'm evil...but this is worse'' card.
5. The quest giver can offer a good bribe and reward to make it worth it (or even a curse or such too)

[Zanos]

Most PCs aren't going to be able to kill a demon lord. We're really talking about the PCs not attacking something they can't kill and don't know what it is.

The Dwarf being a servant instead of the demon lord itself is a good idea, the PCs off the servant and everything is fine.

[Fizban]

Ah, Expedition to the Demonweb, yeah that one's pretty dumb. I kinda wanna say the answer is "just don't run it," but that's not much of an answer.

So instead I'd say: let him die. Seriously, the guy and his plot are pretty dumb and if your players want him offed then small loss. I feel like there's a sidebar somewhere that gives some suggestions on what to do if they do, just not in a useful place. Making up other trails for them to follow might be more challenging, but would probably be a much more satisfying justification for a sprawling planar adventure than just "some obvious demon told us to do it." If they're 7th+ level by the time they take him out they can just rely on Divination for hints on where to go next, even if you don't have other hooks prepared.

Most of the guy's text is laboriously written as him being run first person with the party, and the build lacks the (quite significant) magic required to carry on a proper projected conversation from safety, but the book is also the source of the infamous mirror mephit of simulacrum abuse fame. You could have that abuse start with the quest giver who controls the mephit summoning spell in the first place, though they'd need to have had scrolls of it in order to pull it off (and the questgiver in question isn't a demon lord, just a demon with some class levels- unless the PCs have discovered the demon lord behind the demon and have gone off the rails and out of their league).

I didn't read the whole thing, but I'd say to watch out for the end: like a lot of the adventures from this area it's pretty swingy, with a custom super demon and a potential "PCs fight everything at once" situation, with the campaign drawing monsters from books all over the place along with classed NPCs that have a good chance of being inconsistent. Maybe not as bad as Scouring of the Land since they're mostly monsters, but still.

[TheIronGolem]

If they kill him, they will loot him. So when they do, make sure they find at least one clue that points them toward the same quest he would have sent them on. A treasure map, a letter from the BBEG saying "Whatever you do, don't let the heroes go to the Catacombs of McGuffin or our evil plans will be ruined!", a magic item whose powers must be unlocked at Castle Plotylvania.

[The Random NPC]

Is this the Expedition to the Demonweb Pits? If so, the letter doesn't actually identify who sent it, you could have the guy pretend he didn't. You could also have some dabus roaming nearby. Also, the bar is chock full of evil creatures, if Rule-of-Three is attacked, they might decide to take out the meddlesomec do-gooders while they're weakened.