Spoiler alert!!
It's technically possible because we never saw his body and Lancelot tries to stop Luceris from killing MC by stating that they're a child, which wouldn't make sense if he'd already killed MC's twin beforehand. Then again it's unlikely Alistair survived the fire. Maybe he's some kind of spirit? It's possible since there are gods and magic and the fact that we hear his voice in the story but probably not.