Ever after.

Afterlife for Avatar can be different than it is for the others. They are free to go wherever they want, but they get the privilege of having their own, private space in their God's dominion/planet. It's like having their own field and manor, just the way they like it. And they can bring there whoever they want.
In BangSul's case, he has his children with him in there and occasionally Goss to visit other people he holds dear.

His afterlife is overall pleasant, if it wasn't for one thing that haunted him for his whole life and even now: all the unfair things he did to WonPil and causing his death.
When BangSul died, almost 1000 years after, he was still tormented by all that and the fact he was never even able to make up for it.
After his final sacrifice, together with Wuning, he was welcomed to the Halls like a hero. He sure did a lot of sh*t in his life, but the good deeds were far more than the bad ones, in the end.

BangSul tried to look for WonPil almost as a first thing, even before looking for his own children, but there was no way. For absolutely unclear reasons, the Gods never allowed him nor anyone else to see WonPil in the Halls. Not even WonPil's own children, which alone makes it clear that it was not WonPil's will. But the Gods didn't clarify the matter, despite being questioned by him, Elton and HaoLin a lot. In the end, only the Gods will know their reasons for that.

Almost one century after his own death, BangSul finds out that WonPil was actually reborn and from that moment on, he has been watching over him from a scrying pool in his garden. He couldn't do anything to make up for him when he was alive and couldn't even see him to talk after death, so he at least wants to try to do something now.
Naturally he also allows other people who loved WonPil in his first life to come to see him from his scrying pool and TiShan, Elton and HaoLin have basically moved to stay there with him to be able to see their father whenever they can. Especially Elton, he is basically spending the entire eternity by that pool.

Of course there is not much he can do from there, he can't directly speak to the living or use magic, but he can try to communicate with WonPil through other means, like dreams and animals.
What he really wants is WonPil to have his gifts. There is literally no person alive he'll allow to take the top of his spear and his necklace.
When he finds out that WonPil is even staying so close to Muhan, his attempts to make the boy reach it become more constant and insisting. He tries to contact WonPil every time he sleeps, in different ways and forms, always with the purpose of trying to guide him to the spear head. It's frustrating, because dreams aren't easy to work with and most of the times they are forgotten before the person even wakes up. BangSul wishes he could just possess WonPil to bring his body there, but it's obviously not in his possibilities.