Realistic isn't so cut & dry. We have no idea why the narrative was that AD wasn't going to re-sign in Boston. His agent spoke about it, saying AD preferred LA or NY. His dad spoke about it, saying Boston showed no loyalty to Isaiah Thomas and that's why he didn't want AD to go. But you could change the narrative.
Tatum's contract becomes the issue with the trade. He only makes $6.7M this season and $7.8 the next. Davis is at $25.4M now and $27.1M next year. You''re going to have to get Boston to give up an extra $17-19M to make the trade work and at that point, how willing would Boston be to empty the chest in hopes that the success they have would convince AD to stay?
You could always add a 3rd team into the trade, making a variation of the Lakers trade. Here's a few ideas.
NO receives: Ingram, Kuzma, LAL 2019 1st Rd pick, PHX 2019 1st Rd pick
LAL receives: Davis
PHX receives: Ball
NO receives: Knox, Robinson, Smith Jr., NYK 2019 1st Rd pick, NYK 2021 1st Rd pick, NYK 2023 1st Round pick
NYK receives: Davis
NO receives: Hayward, Tatum, BOS 2019 1st Rd pick, MEM 2019 1st Rd Pick (moves to 2020 if MEM pick falls inside Top 3)
BOS receives: Davis, Moore
* technically this can work because I don't believe the rule preventing Davis & Irving being on the same team before the off-season is in the game
NO receives: McCollum, Collins, POR 1st Rd Pick
POR receives: Davis, Payton
My personal favorite
NO receives: Middleton, Bledsoe, MIL 1st Rd pick
MIL receives: Davis