Imagine you’re baking a cake. The recipe calls for two eggs. Once you remove the cake from the oven, if someone were to ask you, “What happened to those two eggs?” you could reply that they are in the cake. But unless you’re a particularly terrible baker, you would not be able to distinguish the eggs from the other ingredients in the cake. You could say only that they had assimilated into the entire volume of the cake.
Now imagine the cake is the universe. Once you Vanish the eggs, their matter permeates the universe, but they no longer exist as distinct objects. Therefore they are at once part of “nonbeing” and “everything”.