Warning! Spoilers for Thanos (2018) below!
In one Marvel Comics reality, Thanos wins, and what he does with the heroes he's captured and killed is so disturbing, that there's no way the Marvel Cinematic Universe could even consider the storyline. In the "Thanos Wins" series, the Mad Titan successfully destroys all of his adversaries and ultimately feeds them to his pet, the Hulk.
Thanos has successfully defeated the Avengers and other heroes across the Marvel Universe before, but no victory was as destructive and thorough as his triumph in Donny Cates, Geoff Shaw, and Antonio Fabela's Thanos series. The series sees Thanos transported to a dark future where an older version of himself has conquered reality. He learns that King Thanos has killed practically every single being in the galaxy, but still pines over Death. The Cosmic Ghost Rider tells him more about how the future version of the Mad Titan came to be - revealing that he's kept one longtime Avenger alive in the Hulk.
In Thanos #15, the Cosmic Ghost-Rider reveals that Thanos has kept the Hulk as his own pet and fed him his former teammates - including Captain America. He shows Thanos the prison where the Hulk is kept - and it's pretty gruesome. Among the heroes seen in the bones include the helmets of Thor, Antman, and Nova, Wolverine's claws, and Doc Ock's tentacles. Thanos had clearly used Hulk as his own personal garbage disposal for anyone who threatened him. It's particularly sad because the Hulk doesn't want to continue his existence as King Thanos' dog, as the first words he utters to Thanos to "kill... Hulk?"
It wouldn't be until the Fallen One (Silver Surfer) freed the Hulk from being King Thanos' pet, that things would get even more tragic. Now an old and decrepit Bruce Banner, he still begs to be killed. With tears in his eyes, he tells the Fallen One, "please don't let me hurt anyone... please..." Unfortunately, Thanos and King Thanos would team-up to kill both the Fallen One and the Hulk.
Among the many dark timelines that Marvel has introduced, there are few that are more disturbing than the one where King Thanos rules. King Thanos is hellbent on ruling everything no matter what the cost. Feeding Marvel's top heroes (and some villains) to the Hulk, who just wants to die, is extraordinarily tragic, as he just wants his existence to be over so he doesn't have to experience all of the violence and trauma. But King Thanos made him his own personal monster. There's no way the MCU could ever adapt this story. Thanos' ultimate victory is far too disturbing.