Followers at 0 HP

When a follower is reduced to 0 HP, their fate is in your hands. If the source of damage was potentially lethal, then they're out of the action and you pick 1:

• They're dead, immediately
• They trigger Death's Door (even if they weren't directed to by their PC). Their PC's player rolls
• They're dying, and will either die or trigger Death's Door soon if no one intervenes

Remember: it's not your job to protect your NPCs, and followers are NPCs! Let things burn.

If the source of the damage wasn't lethal, then the follower is out of the action until you say otherwise or they regain HP (because of magic, someone's move, or because someone tends to their wounds and they Recover).

Note: a Ranger's animal companion is an exception. They get a special move, Loyal to the End, that dictates what happens when they reach 0 HP. No one wants to see the dog die.