First, is the True Patronus really that overpowered? We know that it can be used to destroy Dementors, but that is a very specific limited purpose and will have no value after The Great Dementor Hunt.

Do we know where Dementors come from? Could it be possible that the Killing Curse creates them?

I don't think that the True Patronus is going to be an easy way to bring the end of death. It would not do it on its own and would probably be much harder than figuring out how to kill dementors.

It can be used to block the Killing Curse, but Quirrelmort probably is smart enough (and has been around Harry long enough) to make use of some transfigured depleted uranium slugs and a Mass Acceleration Charm. Or fire. Or lightning. Or anything, really. It merely neutralizes another seeming game-breaker. (While Mad-Eye Moody's description makes it sound very powerful, but I don't know if anybody has ever actually used it through all barriers or over intercontinental ranges, and the ability to dodge it indicates that it cannot be THAT good of a homing spell.

Here is an alternative interpretation of the prophecy:

THe one: Harry With the power: The True Patronus To vanquish the dark lord: The Dark Lord is not Voldemort, but rather a personification of death (maybe even a literal personification of death such as the grim reaper as a King Of Dementors. approaches, born to those who have thrice defied him. :Heroism is often called 'death defying'. Alternatively, it could be a wierd interpretation with Harry being born from his biological parents to his adoptive parents. His adoptive father is a biochemist (IIRC) who works in a field that is probably connected to medicine. Perhaps he has made three significant medical discoveries? Although I am not sure about the whole thing with being marked as his equal or whatever.

Wouldn't that make Quirrelmort an ideal candidate for stonemaking?

No, I was really, really unclear. The way I see it: Mudane Patronus: A powerful but non-general preference for life rather than death embodied in a desire to protect. True Patronus: A fully general preference for life over death Avada Kedavra: A non-general preference that a specific person die Hypothetical Apocalypse Spell: A fully general preference for death over life. It's unlikely that anybody would ever cast this. Possibly connected to the ritual that will summon death itself? Ritual to summon death itself: True Patronus may be the counterspell to dismiss death. Horcrux: Requires a selfish preference for your life to exceed your acceptance of the sacrificial victim's preference. Philosopher's Stone: Possibly requires very difficult magic and an explicit,non-general but non-selfish preference for life over death.

I think that using the True Patronus charm to end death might (some or all): A) not end death by itself, but open the door to a magical, Muggle, or combination immortality method B) lead to the discovery of a higher-level method of operating the Atlantis system, letting one use magic to directly fulfill any preference C) Re-activate a latent immortality function in the Atlantis system. It won't be easy, or a plot-breaker.