We had two close calls while running Curse of Strahd. First was the ambush >!at the coffin maker!<. Which ended with 1 pc fully dead, one still standing and the rest bleeding out. While two >!vampire spawns!< where still standing. At this point I was not willing to fully kill my party, so the healthier of the >!vampire spawns!< Kidnapped one of the PCs for a private Date with strahd. That's was barely enough to let them survive the encounter

The second time was the fight against >!Bab Lysaga!< In berez. Multiple people told them, that this area was extremely dangerous. They didn't listen. The boss showed them really quickly that the rumours were true. Then the >!house of Baba lysaga!< Awoke and dropped one of the PCs. At one point I stopped the game briefly and flat out told my players: "this is a potential TPK, watch what you are doing". Two PCs choose to heroically sacrifice themselves to give the others a chance to escape.

Both events echoed through the entire campaign