NPC Death

What happens when an NPC dies? Do they ever come back to life, or gone from the game?

Are you asking about one that you have to save, like say Old Mack? They come back when you exit the area.

that quest really pissed me off.

first time I couldn't find him at all (because *edited for spoiler content*) even though I was standing right on top of the green star, second time I was convinced his buddy had eaten him.

The quest Wayward Wizard. The NPC I had to talk to Orion, and then he started walking away. Some bears started to attack him and killed him.

Oh, he comes back later. Maybe Lina the Healer ressed him