If they do Abby's backstory before Joel's death then it'll give context to her motives but it will also greatly diminish the impact the narrative has on the audience. I personally think an in-tandem where we play out the events happening in Jackson side-by-side with Abby culminating with a mid-point finale as Joel's death then the aftermath of that playing in the second half of the season would be the way I'd like to see it go down. The other option I see floated is to follow Abby's story for the entirety of Season 2 with it culminating in the realization that Joel is the person she's hunting, allowing the Season 3 opening to be the back half of TLoU2. But Druckmann is heavily involved in this project so I think he's going to insist that the show play out very similarly to the game.