One detail from the Buu Saga makes Android 16 still being dead a Dragon Ball Z plot hole. Android 16 was one of two major characters to die at the hands of Perfect Cell during the Cell Games. Both he and Future Trunks were killed by Perfect Cell when the villain was trying to motivate Gohan into using his full power.
Most of the havoc unleashed by Cell in Dragon Ball Z was undone at the end of the story when the Z-Warriors made their wish to Shenron. With Android 17 and Android 18 on different occasions, they don’t seem to have the ability to restore 16.
Android 16 still being dead in the anime has long been attributed to the fact that he’s more of a robot than a real android, but a reveal in the Buu Saga contradicts this claim. When the Dragon Balls were used to bring back everyone slain by Majin Buu when he destroyed Earth, a montage was used to reveal a number of forgotten Dragon Ball characters who were affected by the wish. Among them was Android 8, the Red Ribbon Army android from the original series whose design was inspired by Frankenstein’s monster. Android 8, like 16, doesn’t share the human origins of 17 and 18 and was built entirely in Doctor Gero’s lab. If Dragon Ball Z's Android 16 can’t be brought back because he’s just a robot who doesn’t possess an actual consciousness, it shouldn’t have been possible for 8 to be revived either.
How Android 16 Can Return In Dragon Ball’s Future
Dragon Ball Z resurrecting Android 8 but leaving Android 16 as one of the anime’s fallen heroes is a plot hole – but not one that can’t be fixed. A future Dragon Ball movie or show can reveal that even though 16 has been counted as dead for more than a decade now, 16 was revived by the Z-Warriors’ wish off-screen; his resurrection just wasn’t shown. A retcon can confirm that 16 has been wandering the Earth in secret for years. It could be that 17 and 18 have been oblivious to his survival all this time. Or, they did know about it and it just wasn’t discussed when they met in Dragon Ball Super.
An alternative solution is for the anime to simply create a new version of Android 16. If the new Red Ribbon Army or some other group was able to salvage what was left of its body after Cell killed him in Dragon Ball Z, the robot could be brought back online, possibly as a villain with a new mission. Depending on what happens with his story, the anime might get a chance to make him a proper Z-Warrior and have him fight side-by-side with Android 17 and Android 18 again.