In the comics, one of the great gimmicks of the Suicide Squad books (especially early on) was that characters died all the time. Before Harley Quinn came along and became the star of every Suicide Squad comic, waiting to see who would die was basically the whole thing. David Ayer’s movie paid lip service to that with boring nobody Slipknot blowing up after deciding to see if the whole “we put a bomb in your neck so you’d follow the rules” thing was legitimate and Diablo let himself get blown up, but—possibly because that movie isn’t very good—those didn’t feel like particularly impactful deaths.
For his The Suicide Squad sequel/reboot thing, though, director James Gunn is teasing a proper series of big-name characters getting taken out. On Twitter, he recently noted that DC Comics gave him “carte blanche” to do what he wanted with the movie, saying one of the things he wanted the company to agree to before he signed on was that “no character was protected by DC.”
In other words, Gunn says he can kill whoever he wants to kill in his movie. So… Harley Quinn? That seems unlikely, no matter what he says, but it’s not like the DC movie universe is as tightly locked-down as the MCU. Harley could die in The Suicide Squad and still come back in Birds Of Prey 2 without really causing problems to the “canon” because the “canon” is already a mess.
In a subsequent tweet, Gunn added further fuel to the speculation fire by asking his followers which “two characters” they think are most likely to survive. Not which two will die, but which two will live, implying that a lot of them are not going to make it. The new Empire cover included in Gunn’s tweet is handy primer on the movie’s wacky cast of characters, all of whom now seem equally likely to meet some wacky end in the movie.