Winning combat in turn-based classic RPGs is a challenging job, but losing a team member for any reason could cost you a lot, especially when you are already outnumbered in a battle.
No matter if your companions are downed or dead, there are multiple ways in Baldur's Gate 3 to bring them back to life. From paying a bunch of coins to spelling special magic, you can revive your teammate during combat or after that.
How To Revive Downed Companions
If your companion is down, but not dead yet, bringing them back will be much easier. When a character is down, you will spot a hand icon above their body, which indicates that they are not dead yet, but if they receive more damage from the enemies, they will be dead eventually.
As long as a companion is down, any healing spell from other characters that can be applied to a companion will revive them. This is the fastest way to revive a downed companion without reaching out to them.
However, if you don't have such a spell, you can use the "Help" command, which requires an Action Point represented with an icon of two hands holding each other. If you select this action and implement it on the downed companion, your character can revive them upon standing next to them.
How To Revive Dead Companions
If a red skull appears next to a companion's icon, it means they are dead. While it is still possible to revive dead characters during combat, that requires you to have a special item called "Scroll of Revivify". Each character that has at least one instance of this item in their inventory, will be able to use it similar to a spell on a dead companion to revive them, both on and off combat.
Some companions, like Gale, have a special quest for reviving them. In Gale's case, for example, a replica of his soul will appear after his death, revealing the quest and steps you need to take to revive him.
Other than that, there is also an NPC in Baldur's Gate 3 that can revive any of your companions in exchange for some amount of gold. Withers is a mysterious character that will join your camp after you set them free of a coffin inside a chapel on the eastern side of Roadside Cliff fast travel station or on the north of the Overgrown Ruins fast travel point. This is a quest of its own that you will only discover upon exploring the chapel, but once you bring Withers back to life, you must avoid killing him, so that he can join you when you set up your camp the next time.
When you visit Withers in your camp, you can ask him for services he can provide, and then he will tell you that he can bring back dead people to life, but he will ask for 200 Gold for reviving each dead companion.