In the Series, planes are softly placed right in the middle of a Manhattan intersection and we're never shown if the planes are returned to the sky. Considering there is no way to taxi the plane out of the city, imagine the gridlock that would have happened before the plane was finally removed, probably by cutting it up.
The Overlords are extremely careful about even hinting at what's going to happen to humanity, right up until the children's powers have awakened and they've floated up into the sky, safely out of reach of their mortal elders. Could they have made the mistake of revealing the truth to some other species while their offspring were still ordinary, only for that species to exterminate their own children in an attempt to keep the Overmind from consuming their heirs and world?
Even more alarming thought: could the Overlords themselves have done such a thing when their own offspring began to express feelings and abilities their elders didn't understand, and that's the real reason the Overmind judged them unsuitable for assimilation?
In the final moments of Earth, as Milo begs Karellan to keep some memory of Earth alive so Humanity isn't left forgotten, Karellan plays the classic music Milo remembers from his childhood. After the Earth is destroyed, Karellan leaves it behind for some future wanderer to find. Only, at this point, the viewer knows that there will be no future wanderers. Only the dead end species who work for the Overmind end up traveling space, and they are numb to the deaths of civilizations. Earth and Humanity die, forgotten by all, simply one mind among thousands to ascend to the Overmind.
The Overlords' diabolic appearance is much more blatant in the series than in the original novel. While this detracts from their originality, it also makes a certain amount of sense: the opening of the series is set in the present, not the 1950s, and scifi and fantasy have concocted so many other winged humanoid races by now that the original Overlords would probably have reminded people of one of those species, not medieval demons.
Well, it certainly would explain why SETI hasn't found any alien civilizations yet if civilizations tend to join the Overmind before stepping off into space.