It's possible that The Walking Dead will delve a little deeper into Negan's backstory. The show's producers have indicated they have a "willingness" to explore the character's life before the world ended. After two seasons of being a thorn in the side of Rick and company, Negan was finally defeated in the season 8 finale. In a drastic change of the status quo, Rick opted to keep him as a prisoner back in Alexandria instead of killing him.
This is fairly similar to what happens to Negan in Robert Kirkman's The Walking Dead comics, which has subsequently explored Negan's past. Readers have seen him go from a foul-mouthed gym teacher to a grieving widow to the leader of The Saviors. Now that "All Out War" has concluded, Walking Dead fans are curious if Negan's story will be seen on-screen in future seasons.
When answering questions in its weekly fan mailbag, Skybound indicated that The Walking Dead producers have "expressed a willingness to dig deeper into his past." So far, the series has shown nothing of Negan's life prior to The Saviors. However, the little bit that Negan's revealed does sound pretty similar to his comic book origins. At different points this past season, he had talked about his past to both Father Gabriel and Jadis. With The Walking Dead season 9 now filming, it's possible that we could see more of Negan's story on the small screen in the near future.
After all, The Walking Dead has never shied away from shuffling its timeline around. When the Governor was reintroduced in season 4, he got a run of flashback episodes that painted him in a new light; for a little bit, at least. With Negan sticking around, the show will need to find a way to make him appear a bit more sympathetic, given Carl can no longer serve as his outlet. One way to do that would be seeing him as a grieving husband just before the apocalypse. Depending on how closely the show adheres the comics, there could be a two-year time jump between seasons 8 and 9... or 9 and 10. And assuming Negan remains imprisoned for that long, he wouldn't have much to do other than reflect on his past.
It's worth mentioning that Negan's presence creates another problem for Rick. His decision to leave Negan alive didn't sit well with Maggie at all. She still wants vengeance since Negan killed her husband, Glenn. The fact that Lauren Cohan won't be in as many episodes next season might indicate that things could go south for her character. In addition to the pending civil war within Rick's ranks, the season 8 finale might have covertly introduced an all-new Walking Dead villain to deal with, which is where Negan could end up proving useful. He's been a formidable opponent, so the possibility of him forming uneasy alliance with Rick is intriguing to say the least.
The Walking Dead season 9 is expected to premiere in fall 2018.