That means that even though the explorers were dead when I opened the game back up, they had only died a few moments ago rather than several weeks ago, so the 24 hour body decay hadn't completed yet. My theory for all of this is that the game does not actually run in the background, it just saves timestamps, then calculates what happened the next time you open up the app. I also had some dead bodies lying around that did not decay after 24 hours. I am bringing them back to the vault and renaming them Bear Grylls and Les Stroud. They were not anything fancy, just some level 1s with terrible stats that I sent out to die. I left my explorers in the wilderness, and some survived! I shut down fallout shelter and did not reopen it for 4 weeks. While the other answers are accurate, I actually have done this.