Tragic idea for Stranger Things season 3:
Instead of getting better, Billy actually progressively gets worse, to the point that he ends up becoming a legitimate threat to everyone. In the season finale, with no other option, Steve is forced to kill Billy in order to save the group.
Steve then ends up going on the run for Billy’s murder. Then, as a favor to El, Kali agrees to take Steve in with her crew, leading into season 4.
That’s how Season 4 starts, with Steve and Kali’s crew on the run from the police.