Billy Hargrove's arc in Stranger Things was expertly accomplished across seasons 2 and 3, with his role as a villain teased and built gradually. Billy became one of the show's most compelling characters because to Montgomery's portrayal, and the character's redemption at the end of Stranger Things season 3 was one of the show's most gratifying moments. Despite the fact that Billy's death is an evident roadblock to his comeback in Stranger Things season 4, the trailer hints at his significance to the tale, leading to speculation that he might return.
It's unclear how Billy can return, but the suggestion is that his tale on Stranger Things isn't over yet. The teaser depicts Max's anguish over her brother's death and includes a view of Billy's grave, as well as a reference to him in one of Stranger Things season 4's episode titles. All of the evidence points to Dacre Montgomery's reappearance as Billy Hargrove in some manner, however it's unclear if this is due to his potential survival or a simple flashback.
Stranger Things season 4 will have an episode named "Dear Billy," which Max also says in the trailer as she tries to reconcile her conflicted feelings towards her brother. This would make Billy's Stranger Things return more than likely a flashback sequence of some kind, which would suit with Max's evident attempts to move on from Billy's sacrifice. It's probable that a flashback sequence will be used to explain issues regarding the siblings' background, such as why Billy and Max moved to Hawkins in the first place.