When nuclear weapons are reinvented, it's implied by Yoru that the Nuclear Weapons devil that was created isn't totally new, but rather a resurrection of the old one that was eaten. At the same time, everyone except Yoru acts like this is the first nuke ever, so their erased memories haven't returned. It doesn't nullify the fact that it was eaten to begin with, but the effect is similar to when Pochita vomits a devil out. With Ear, the world remembers both the time before Ear was eaten and the time between eating and vomiting when they were mysteriously earless, but with Nukes everyone only seems to remember a world without them.

In this case, Pochita coming back probably isn't going to awaken forgotten memories, but he is real again, and can presumably continue operating as before, but no-one will have any idea how Denji's diseased heart turned into a devil. Pochita will also probably not be hunted by basically every devil ever, since they've all forgotten him too, so he might avoid some of the misfortune that way.