Strictly speaking Heb 12 says the discipline is given to those whom the Father intends to inherit. That doesn’t necessarily mean they have come to the faith already. But most of what the Hebraist has to say about punitive discipline (including later in Heb 12), is aimed at backsliding Christians, who aren’t in fact being faithful but who are being intentionally treacherous instead.
The upshot is that whomever God disciplines, God intends to inherit.
Neither do I. “Fire” is a figurative term for God’s LOVE. Nevertheless, those who resist that LOVE will experience it as pain.
The Orthodox Church holds that everyone ends up in the presence of God after death, and that His children experience Him as Heaven, and those who rebel against Him experience Him as Hell.