Gotham City is one of the most dangerous cities in the DC Universe. Batman has dedicated his life to fighting crime. Over the years he's had Robin as a sidekick, but there have actually been several different people behind Robin's mask. The biggest danger used to be having to go out in public in short-shorts and pixie boots. Now the biggest threat is the fact you will eventually die when you take on the mantle of the Boy Wonder.
In Batman #16, the Dark Knight realizes his old enemy Bane will be coming to Gotham, seeking revenge, after Batman's attack on Santa Prisca. Batman asked his former Robins to leave town and stay out of the fight. Of course, they decide not to follow this order. Before we get into what happened in Batman #16, let's look at the previous times the different Robins have died.
There will be spoilers for Batman #16.
Jason Todd - Batman #428 (1988)
Jason Todd was the second Robin. When he discovered his birth mother was still alive, he tracked her down. Unfortunately, she was blackmailed into working with Joker, who beat him nearly to death with a crowbar. He then blew up the building where he left Jason and his mother just as Batman arrived to witness the explosion.
Jason was later resurrected through some reality-altering effects (courtesy of Superboy Prime) and one of Ra's al Ghul's Lazarus Pits. He had a pretty big chip on his shoulder since Batman allowed Joker to live after he died. They eventually came to terms with the situation.
Stephanie Brown - Batman #633 (2004)
Stephanie Brown is better known as Spoiler. She had a brief stint as Robin and returned to her Spoiler guise. During a big gang war in Gotham, she suffered grave injuries and apparently died as Batman sat by her bedside.
Later, it was revealed that Dr. Leslie Thompkins faked Stephanie's death. Her identity had been compromised during the fight and the two left Gotham to perform volunteer work in Africa. Batman suspected she hadn't actually died but didn't have concrete proof. This is why he never built a memorial for her in the Batcave.
Damian Wayne - Batman Incorporated #8 (2013)
Damian Wayne is the son of Bruce Wayne and Talia al Ghul. Raised by the League of Assassins, Damian eventually came to live with his father and took on the mantle of Robin. When Talia unleashed an attack against Batman and Gotham City, Damian fell victim to the Heretic, his artificially aged and genetically enhanced clone.
Damian was resurrected with the Chaos Shard, a powerful and magical crystal that once belonged to Darkseid.
Dick Grayson - Forever Evil #7 (2014)
4Dick Grayson was the original Robin who took on the identity of Nightwing years later. Nightwing got captured by the Crime Syndicate, an evil version of the Justice League from an alternate Earth. His identity was publicly exposed, and he was later attached to a nuclear bomb. The only way to disarm the bomb was for Grayson to die. Lex Luthor, working with Batman, caused Dick's death with a pill that paralyzed the cardiac muscles around his heart. He was revived with a shot of adrenaline.
Grayson may not have completely died, but everyone was lead to believe he did. Batman needed Dick to go undercover to infiltrate the Spyral organization which had targeted the superhero community. Dick spent some time as a "spy" until he returned to his Nightwing persona.
Tim Drake - Detective Comics #940 (2016)
Tim Drake was the third Robin. He deduced Batman's identity after the death of Jason Todd and convinced him Batman needed a Robin to keep him in check. When a military group known as the Colony targeted Batman and Gotham, Tim hacked into their system to redirect hundreds of attack drones that would have killed innocents. He defeated the first wave but was vaporized by the second.
Batman and his allies have mourned Tim's death, but it turns out he was actually teleported away and kept prisoner by the mysterious Mr. Oz.
Dick, Jason, and Damian? - Batman #16 (2017)
Returning to the current comics. Bruce Wayne ordered Dick, Jason, and Damian to leave as he helped Gotham Girl in her recovery and prepared for Bane's arrival. Entering the Batcave, he saw three dead bodies left hanging. It appears the three Robins are now dead.
Of course this likely won't be the case. Bane probably found three innocents with similar body types and left them there as a warning to Batman and to rattle him.