At the end of Interstellar, it's revealed that mostly unseen character Edmunds has died after sending a positive signal back to Earth to alert them that his planet is viable for humanity, but how he died is never shown or explained. Interstellar’s ending contained several revelations and went by so fast that many were left wondering how the character Edmunds had died. One of the original members of NASA’s Lazarus mission, Dr. Wolf Edmunds is sent to visit one of twelve potentially viable planets to host humanity after Earth has become inhabitable due to pollution. Prior to the mission, he is known to have had a romantic relationship with another scientist, Amelia Brand. Brand is not part of the Lazarus mission, but takes part in a mission taking place several years later to visit the planets that have been signaled as positive — that mission, aboard the Endurance, is the complex and cerebral sci-fi plot at the heart of Interstellar.
Edmunds is one of three positive reports that the crew of the Endurance receives. His data is very promising, but his transmissions were interrupted at some point in time and it’s unclear if he’s still alive. Because of his romantic links to Brand, the crew thinks there may be bias behind her desire to visit him first, which contributes to the decision of Endurance’s crew to not visit Edmunds before the very end. Brand, who is one of the strongest female characters in Christopher Nolan’s films, ends up visiting him alone as a last chance at survival, since the other two planets were not, in fact, viable. The ending shows her mourning and crying in front of Edmunds’ grave, which she identifies with his tattered name tag.
Interstellar is a polarizing movie, and while the circumstances of Edmunds’ death are not explicitly stated, the background action gives the audience enough clues to be able to guess the cause of his death was probably a deadly rockslide that destroyed his pod and equipment. It is stated at the beginning of the film that he gave a “thumbs up” signal to alert Earth that his planet was viable. After assessing the planet’s conditions and completing his part of the mission, he would have gone into hypersleep to await the rescue mission, settling into his pod at which point it is suggested he was killed.
In Interstellar's final scene, as Brand arrives on the planet and learns of his death, CASE, the robot accompanying Brand, is shown digging through debris. Rocks and dirt cover what used to be Edmunds’ pod, which is badly damaged. The grave Brand builds for him is also composed of rocks, also seemingly taken from the wreckage. Implicitly, the movie shows the audience that a landslide destroyed his pod, most probably killing him in the process. It is true that sci-fi movies often get things wrong about the physics of space, but this particular landslide is not one of those - a natural disaster such as this one would have similar consequences on Earth.
If the landslide is not to blame, then time, which Nolan loves to manipulate, is the likely culprit. The system to which both missions travel is orbiting a massive black hole called Gargantua, and its gravity affects space-time. More specifically, it dilates it determining that time spent on different planets of the system is not equivalent to time going by on other planets or Earth. By adding up all the years the Endurance ends up wasting by visiting the two planets before Edmunds’, it adds up to around 80 years. Considering Edmunds was at least 30 years old when he left on the Lazarus mission, he would probably have died of old age long before Brand arrived. Nevertheless, even if it wasn't the cause of death, the landslide still explains why his data transmissions stopped abruptly after a few years — the pod’s equipment was so damaged that it stopped functioning. Interstellar's ending is set up in a way that it could easily be given a sequel, in which it is explained in better detail, but no such projects have been announced. While it is a tragic end for both Edmunds and Brand, she can be certain that he died peacefully, having completed his mission successfully.