In Baldur’s Gate 3, companions can consistently be revived using the revivify spell or Withers’ services, meaning players often won’t worry about losing their favorite characters. Despite this, there are several different ways for companions to leave the party. The most common way players will probably experience this is through loss of approval – if the player makes too many decisions that a companion disapproves of, then they will no longer want to travel with them.

https://screenrant.com/bg3-all-choices-companions-leave-party/