Baldur's Gate 3 is full of characters with their own stories and goals, but that doesn't mean that the main party will end up crossing paths with all of them. There's a set of NPCs in the game that most parties will likely never meet due to the specific roles the developers at Larian Studios gave them. Even if these characters are generally never seen, their existence shows how much thought and preparation went into BG3 to handle just about any scenario.
[Warning: The following article contains spoilers for Baldur's Gate 3.]
When a game requires characters to fulfill a certain role, the developers will usually create fail-safes for the event that an NPC is killed before they complete their role. Fail-safes are NPCs who will take the place of another character if that character dies so that their role is still filled, and Larian Studios included fail-safes in Baldur's Gate 3, but they don't appear in most playthroughs since it's usually not necessary. Below are ten characters who are generally unknown in BG3 because they rarely show up in playthroughs.

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10 Asharak
Zevlor triggers the celebration party at the end of Act One when the Goblin Leaders are defeated, but it's possible for Zevlor to be killed before this point in the game, making him unable to cue the festivities. Luckily, Larian Studios created a fail-safe NPC who replaces Zevlor and allows the Tiefling celebration to occur at camp. Asharak expresses regret that Zevlor wasn't able to celebrate the fall of the Goblin Leaders with the rest of them, but the act continues on unhindered by his absence.
9 Cerys
Cerys is part of the game in Act Two, but she only appears in Act One in certain circumstances. Since Asharak can be found in Emerald Grove, he can also be killed along with Zevlor before triggering the Tiefling part. If this happens, then Cerys appears and starts the celebration for the party. Normally, Cerys can't be found in Act One, and this makes sense considering she's already a fail-safe for a fail-safe, so it's better to keep her safe to fill this job.
8 Kivak
Kivak is the replacement for Ikaron, one of the many Tiefling refugees at the Emerald Grove. Ikaron doesn't have a job like Zevlor, but he can be killed before the celebration for the deaths of the Goblin Leaders. To help prevent the party from seeming lackluster due to the deaths of characters meant to attend, Kivak shows up in place of Ikaron to enjoy the festivities.
7 Rhys
Rhys is enthusiastic at the Tiefling party, cheering to forget Elturel and cursing the Goblins that caused so many issues for his people. However, he won't appear in most playthroughs because Rhys can't be found hanging around the Emerald Grove with the other refugees. But if Tieflings are murdered in the safety of the Grove, Rhys might show up at the party as an attendee to fill in for a party-goer who's no longer able to make it to the party.
6 Vatas
So, Danis has died before he got the chance to celebrate the death of the Goblin Leaders and the news that his people can continue their journey to Baldur's Gate with fewer threats. Well, the party doesn't have one less attendee as a result of Danis' death. Instead, Vatas shows up to take his spot and expresses gratitude for letting them party at the campsite, and that the Tieflings will need to return the favor in Baldur's Gate.
5 Kavil
Considering the number of Tieflings at the party, and how they can be killed while in the Grove, it's not surprising that there are a lot of fail-safes that Larian included to keep the party lively. Kavil is among those fail-safes, and she generally isn't seen in the game. However, male Tieflings aren't the only ones at the party, and Kavil is one of the female fail-safes to keep the gender ratio the same at the celebration.
4 Zae
Lakrissa is close friends with Alfira, but it's possible to kill her as well when she's at the Grove. If Lakrissa is dead, then Zae will replace her at the camp's celebration party. However, Lakrissa's absence probably dampers Alfira's partying spirit given their close relationship.

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3 Gerson The Bent
Unlike others in this list, Gerson the Bent isn't a fail-safe that replaces a different character in the event of their death. If the last Goblin Leader is killed while a party member is still at the Emerald Grove, Gerson the Bent shows up in a cutscene to announce that scouts reported the last leader's death. It seems that Larian Studios thought of every possibility, and small details like Gerson make Faerûn feel alive.
2 Chell
Chell is the fail-safe for Alfira, but only for runs where the Dark Urge isn't the main character and Alfira has been killed in the Grove, not camp. In this case, Chell shows up to the party in place of Alfira. But similar to Zae, Chell's presence means Lakrissa is likely having a worse time because Alfira isn't there with her. If the Dark Urge is the main character and Alfira is dead at their hands, Chell won't show up, and Lakrissa will be worrying about not having seen Alfira, wondering where she is and if she's okay.
1 Quill
If the Dark Urge is the main character in BG3, then Alfira will die if she arrives at camp to the group and fight Goblins. However, if Alfira is already dead or unconscious, Quill shows up in her place and requests to the group. This swap isn't perfect, however, as Dark Urge dialogue later in the game still refers to Alfira as the victim, even if she's alive and well.
Considering all these characters are limited to Act One, it's possible there are more hidden fail-safes that haven't been seen from other acts. However, these details show the dedication and attention to detail that Larian Studio put into BG3, even if most playthroughs won't feature these characters. As it stands, there's still so much that hasn't been discovered that it feels like every day has a new reveal for a hidden detail that's been found. As a result, there are plenty of reasons to keep revisiting and exploring Baldur's Gate 3.
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