The problem is that, obviously, *somebody* is going to die. Almost certainly multiple somebodies. The list of people they *can* kill is a lot shorter than "everyone", though:
-Deadshot is Will Smith, and arguably the lead of the movie. It is extremely unlikely they'd kill the main "hero" of the team who they've cast a major box office star.
-Harley Quinn is Harley Quinn, and has a ten year contract. She's safe.
-Rick Flagg is not a massively famous character, but his *role* in the team is pretty much required. Also, they were originally going to cast another big name actor, Tom Hardy. I think he's safe, unless they introduce a character who could take over the "minder of the team" role first.
-Killer Croc is a Bat villain. I don't believe for a second they'd be allowed to kill a Bat villain in a non Batman movie, even a minor one.
-Captain Boomerang has less protection, but he's also a major Flash villain, and Flash has his own movie coming up. I'm dubious he'd be allowed as cannon fodder.
That pretty much leaves Slipknot ( "who?" ), El Diablo ( "who?" ), Enchantress ( "who?" ), and Katana ( somewhat more known, but not connected to anything in the pipeline ). If they decided to be tricksy and not kill Slipknot, they'd need to find a body bag somewhere else, and the options are pretty slim.
