Treat the Orcs as though they are an organized crime family.
If you murder a member of the Mafia, or one of the nefarious narco gangs of the modern age, do you think you'll get away with it? Will there be a bounty out on your head?
Make the party an offer they can't refuse (Movie ref: The Godfather)
A simple way to get your point across is an ambush/encounter with a large enough group of orcs from that tribe that this party can't defeat. The party is to return the contraband, pay a weregild for the death of that orc, and then they owe the current orc chief a favor. The offer they can't refuse is made by the orc tribe chief: Go get me {this Macguffin} and I call off my other bounty hunters! (Let's say he wants a prize bull owned by a lord not far away, as he wants to improve the stock of his cattle herd since his daughter needs a bigger dowry for the marriage to that other orc clan he's been dealing with...)
If they see the group of Orcs again, they'll all want their blood.
Yes, they will. You are not railroading your players if their in-game actions have consequences. As a consequence of their actions, they are now marked for vengeance or death by an orc tribe.
I don't think any persuasion roll would be good enough to dissuade a large group of Orcs from wanting to tear them limb from limb.
Is it fair to have the orcs be too angry to reason with next time they see them?
How can I prevent them from being able to bluff or persuade without the loss of player agency?
Deception/Persuasion checks with disadvantage
Yes, it's fair for the orcs to (at least at first) not be inclined to parley or listen. Attempts at persuasion/deception can, based on these circumstances, certainly be ruled to have disadvantage. You don't need to prevent the party from trying, but they are not guaranteed to succeed simply by trying to persuade or deceive a given group of orcs. You can either
- Set the DC for making a successful check very high (20+)
- and/or apply disadvantage
- During the next encounter where they try to parley with the orcs, provide the party with clues and descriptions that explicitly signal to them that "a
negotiation is not currently an option."
The DM can also decide that circumstances influence a roll in one
direction or the other and grant advantage or impose disadvantage as a
result. (PHB, Chapter 7, "Using Ability Checks")
But you don't need to roll for this. A roll is only called for when a result or an outcome is uncertain (PHB, p. 171, Using Ability Scores). The orcs are certainly upset.
The orcs might want to capture the party to bring them to justice before the orc tribe (Which might be fatal). Or, a band of orcs (calculate the encounter difficulty to hard or deadly) becomes the posse who chases the party down to capture or kill them: wanted, dead or alive! The party are now fugitives.
This isn't a railroad
This response by the orcs is the game world reacting in a rational fashion to the actions of the characters. But maybe a given orc posse can't take them out. (Back to the "offer you can't refuse" idea). The party is in no position to negotiate with the vengeful orcs (to get the tribe to stop sending hit squads out after them) without leverage of some sort. What does the party have as leverage?
- The contraband?
- Some of the orcs (captured) from the posse?
- Something else? (A unique ability the chief wants them to use on his behalf? A paladin who can, for example, cure the disease of his aunt?)
For the party to make a deal, role play the negotiations after they've had at least one group of orcs try to take them out. Put the orc chief in the role of crime/gangster boss who wants what's his, and a little bit more.
A TPK is also a valid response, but use these with great care
If luck is not with them and the orc posse defeats the party or the battle results in a TPK, that's the luck of the dice ... but you can always choose to rule that the orcs stabilize and capture/revive one of the players (or more) to be taken to the tribe and then imprisoned, enslaved, what have you.
Or the whole party gets enslaved. Now the adventure hook is: escape!
Make their mistake part of the adventure.
Ability checks aren't magic
@Ben made a comment about ability checks that is worth capturing here.
Persuasion isn't mind control. The party, or the party face, can succeed at a persuasion check without the orcs doing exactly what the party wants. For example, a success at persuasion calms the orcs down enough or muddies the waters enough that they're willing to entertain the party making amends,
rather than the orcs only pursuing bloody revenge! There are still
consequences, the party face gets to feel like they saved everyone's
bacon, and you get a story hook out of it in how the amends are made.
The DM decides what campaign he runs
While it's true that roleplaying is a cooperative effort, and it's better to find a consensus... Your campaign is yours. It's your world. You decide how it works. So if every ork is evil in your campaign, then it's so. Your players may not like it, but they're not the GM, so there's that.
That being said, while your are certainly free to decide what your campaign is, if none of your players buy-in then you'll be left without players. Try to find out why they want to play a good tiefling or whatever.
Is it mechanical benefit? Take a similar good race and be done with it. If tiefling aasimar is a great option.
Is it love to that specific race? Maybe you can make them half-blood, maybe a spell changed their alignment for good, maybe the stars aligned on their day of birth. They are the solo good aligned tiefling in the world. Every other tiefling should die, and they know it. Resume your goblin-slaying antics.
Is it because they don't want to try something new, or don't think playing the campaign you envisioned will be fun for them? If that's the case, try to focus on telling them why you want to play your campaign and why letting them playing "evil" characters would hinder the experience. If they're in, go kill kobolds in the name of justice. If they're not, you either make a different campaign or find other players. Maybe convincing the undecided to try a first session and making it awesome can help seduce them into your campaign.
Is it because they want to play out the struggle of having an evil nature and a good heart? Well, that's clearly not what you want. Tell them that this will be dungeon-delving monster-slaying and their sentimentalism has no place in your world.
On a final note, in D&D5e alignments are there mostly for historical reasons, it seems. There are fewer mechanical effects than on other editions, no rules to govern when someone changes alignment and a general "flexible alignment policy" in place. They are explicitly told in the player handbook that they can freely choose their alignment. So if in your campaign alignment is rigid and important, say that clearly, because it's not the default setting.
Best Answer
No, that sounds fun and flavourful. I'm picturing Vikings at the moment because it fits really well, but it would be a neat detail for all kinds of made-up cultures.
There will be published adventures that will go contrary to these expectations, and you'll either have to not use them or spend time adjusting them to fit into your setting better.
The big caveat is that there are player types that this would bring either no positive to the game or actually be a negative. Players who are there to mostly roll dice, have fun with their friends, and unwind without having to really think hard (a totally valid reason to play RPGs) won't work well with this, since that play style relies on using more standard RPG tropes and not thinking too hard about them or the setting's internal consistency. If you have a group like this, or even one player like this, running a game like that will introduce more or less significant friction that you'll have to deal with somehow. (Usually, friction means changing what you're doing, or changing who you're playing with. Sometimes the players adapt, but players are less likely to invest the energy to adapt and that's especially true of the roll-dice-and-unwind type of player.)
A lesser caveat is that you will have to think about how this interacts with the D&D spells that can bring people back to life. Is that an offense against the gods too? Or does properly burying the body permanently ensure the spirit's place in the afterlife and you can't bring them back (and those spells don't work)? If this bit of metaphysics interferes with the (somewhat) common trope of D&D being a game where dying is just an inconvenience, then that will require some adjustments too, either to adventures' difficulty or to your players' expectations, as above. On the plus side, if you and your group are sick of death being merely a speed bump (and enough people do dislike that side effect of D&D's standard spells), then that's a feature! It would be for me.
So long as you have a compatible group and you lay this out up-front – which you should do anyway if this is a major part of the players' characters' culture – this should be fine. Adding a reasonable explanation for where ghosts and ghouls come from is the kind of setting design that a lot of players appreciate. In this particular setup, the players may also come to appreciate that it means their enemies will be reluctant to kill them out of hand, too.
As for wealth considerations, in D&D Next you won't have trouble with wealth. Unlike its two predecessors, it doesn't make wealth required for them to meet an expected power level for their character level, because it has mostly done away with the concept of expected power level. (At least, not as part of the "core" D&D Next rules. Stuff similar to 3e's Wealth By Level or 4e's treasure parcels will probably show up in the modular optional rules.) Your suggestions for how to place "adequate" treasure seem eminently reasonable, where "adequate" in a system that doesn't super-care about wealth is defined by how much treasure you think should be coming the PCs' way in a given span of time.