"He's gone... Goku's gone!!"
Future Krillin's life was exactly the same as his main timeline counterpart's life until August of Age 764, when Future Goku used the Instant Transmission to arrive on Earth and kill Future Frieza and Future King Cold (something Future Trunks' arrival in the main timeline altered). Two years later, in Age 766, Goku died from a lethal Heart Virus with no cure and was unable to be wished back, due to the death being of natural cause. Future Krillin was shocked about his best friend, Future Goku's death.
Dragon Ball Z
Main articles: Trunks Saga and Perfect Cell Saga In "Mystery Revealed", Future Krillin makes a brief cameo when Future Trunks explains to Goku about the Android threat and how they were responsible for killing all the Z Fighters leaving Future Trunks as the only Z Fighter alive in his timeline. Because of the Androids killing Future Piccolo which also killed Future Kami, Future Trunks was unable to use the Dragon Balls to wish any of his fallen comrades including his mentor and best friend, Future Gohan, back to life.
In Future Trunks' flashback in "Ghosts from Tomorrow", it is revealed that Krillin was blown up and killed by Android 17's Photon Flash. The only survivor of the battle is Future Gohan, who dedicates his life to avenging his fallen friends.
Dragon Ball Super
In a flashback in "Extra Edition 1" bonus chapter of the Dragon Ball Super manga, Future Krillin is shown fighting the Androids alongside his allies.
"Future" Trunks Saga
Main article: "Future" Trunks Saga Future Krillin's spirit was erased when Future Zeno wiped out all existence to end Infinite Zamasu's reign of terror. His spirit still continues to exist in the new timeline Whis (in the anime) created or by Future Trunks and Future Mai (in the manga).
The History of Trunks
Main article: Dragon Ball Z: The History of Trunks
In Age 766, Future Goku had been stricken down by a deadly Heart Virus that had no cure. Future Krillin, along with the other Z Fighters and company await the news of Future Goku's health outside Goku's House. However, Future Goku passes away, leaving Future Krillin without his best-friend. Six months later on May 12th, Age 767, the Androids attack and Future Krillin is killed by the Androids.
In the TV Special, Future Krillin is shown being attacked by Future Android 17 and Future Android 18, each shooting a Finger Beam at him at the same time. Future Krillin was one of the last Z Fighters to die. He was 31 years old at the time of his death.
- The History of Trunks