Just in case you murder everyone, Baldur's Gate 3 has back-up NPCs—and even back-ups for its back-ups

pcgamer.com:

Baldur's Gate 3 is a game of almost unparalleled freedom, and we all know what that really means: the freedom to murder any NPC you can get your hands on. Usually, the danger of any RPG murder spree is that you might kill someone who's vital to a later main quest event, and end up locked out of progressing. But it turns out Larian's accounted for that by giving certain NPCs back-ups to replace them if they perish—and even back-ups for the back-ups. 

YouTuber Proxy Gate Tactician has taken a deep (and bloodthirsty) dive into the possibilities around the Tieflings at the grove, and discovered some fascinating interactions. Mild Act 1 spoilers ahead.

Normally, if you choose to kill the goblin leaders, Zevlor, the leader of the tiefling refugees, will invite you to a celebratory party. If you kill him before then, however, you still get the invite—another tiefling called Asharak will step in as the new leader, and take on Zevlor's role. 

So what if you kill Asharak too? As it turns out, there's a third-in-line—Carys, a character you normally don't meet until later in the story, will step in. And because she otherwise doesn't appear at the Grove, there's no way to kill her before this moment, so she's the ultimate failsafe.

But it goes even further than that—because the party is attended by tieflings you can meet in the Grove, it's possible to kill the entire guest list ahead of the event too. But even that won't stop the festivities, as all the guests are replaced by new characters you can't otherwise meet, one of whom even has a unique interaction (drunkenly inviting you to dance). 

Though Proxy Gate Tactician goes on to discover that messing with the game in this way can lead to inconsistent dialogue down the line (Carys