Marbles are not a good example because a marbles would all at once fall off the bag when it opens. But the pieces in the “bag” stick together until a force disconnects them.
The object would already consist of 729 parts at a depth of 2 because the original object that consists of one piece is depth 0.
I don’t think that the engine has to handle all parts of all depths after you broke off only one piece of the depth 1 chunks. I believe it is pretty dynamic and only breaks the parts it needs to calculate and display. So this would be more of a worse case scenario that the engine has to handle e.g. all 729 chunks of an object with two depths and two slices for each of the three axis / depth…