You’re given a good bit of leeway during battles in Baldur’s Gate 3 before you or a companion actually bites the dust for good. While in battle, if a teammate does take enough damage to drop, they aren’t dead then and there. Instead, they will be downed with a chance to roll every turn to get back up. If they roll successfully three times, the battle ends, or you use another character to pick them up, they’re good. If they fail that roll three times, however, they will be completely dead. That can be harsh when you’ve become attached to certain characters and want to further their stories, so you’ll be looking for any way you can to bring them back. Thankfully you do have a few options for reviving companions in Baldur’s Gate 3, but just like respeccing, they aren’t so obvious.
Withers is a friendly undead you can find in a secret room in the Dank Crypt found inside the Overgrown Ruins. After finding and speaking to him in his sarcophagus, he will offer you various services, one of which is bringing back any dead companions. He won’t do this out of the kindness of his heart (probably because it isn’t beating) and will charge you a heavy fine of 200 gold to do so. Still, that’s a small price to pay to bring back a beloved character. Once paid, that character will appear in your camp where they would normally be, so there’s no need to go back to their corpse and find them.
The entire use for this rare item is to bring back the dead. Despite being a scroll, these are consumed upon use, and there are only so many in the game. While they can be found very rarely around the world, your only reliable way to get them will be from vendors. Even then, not all vendors will have one, and those that do will charge you out the nose for one. The benefit of this method is that any class can use this scroll. Simply use it in range of your fallen friend, select them, and breathe life back into their bodies. They will only revive with 1 HP, though, so either heal them up or rest back at camp to make sure they don’t just die again right away.
If you chose to be a wizard, Cleric, or Paladin, or have one in your party, then you can learn Revivfy as a spell once you find a scroll. This way you can cast it without having to find more, but there are some drawbacks. For one, Revivfy is a level three spell, so your healer will need to be level five at least to have a level three spell slot to hold it. If you meet the requirements, you can learn the spell by opening your healer’s inventory, right-clicking on the scroll, and selecting learn. This will cost you the scroll, but also some gold. If you have enough, you can learn the spell and swap it into your list of prepared spells.