Although that seems to be the case that is simply not true. Just because something can happen does not mean that it eventually will. If we on earth take a rocket and shoot it off into space it is by no means certain that after infinite time it will be found. It is possible that humans will never leave our solar system and that aliens don't exist at all. Given those two simple condiditions the rocket would never be found. There are many many such conditions that would lead to it never being found.
Really it's even possible for me to go bury a box in my back yard and for it to never be found. It could sit there for 100years then fall deeper into the earth after an earthquake and just plain never be found for example.
The same would certainly hold true in the multiverse of D&D.