If you built your wall out of separate DM brick blueprint “chunks”, then you don’t have to spawn in pieces, they are automatically created when you break them, because you fragmented them previously in the editor.
If you completely break the DM into the end pieces, then the parent mesh is not visible, and anything you do to the parent which was the large “brick” before, is done to all of the child pieces. So you don’t need to access the individual pieces.
The brick blueprint would be responsible for hooking the fracture event, waiting for something like a time delay or pieces to settle, and then disabling physics, collision, and moving itself down the Z axis however far, and finally destructing itself.
Then in your editor, you could take that single brick you built and duplicate it to stack them up. The size of the bricks and how many you need is going to be a balance between how detailed the effect is and how much resources and performance are dedicated to essentially a wall.
You may still want to track the pieces locations in the blueprint of the DM object though. Because just because it fragmented doesn’t mean all the pieces are on the floor. They could be falling or rolling around. So if you just wait a delay, they might suddenly stop in the air and start slowly moving down however many units until just disappearing. If you track all the pieces, you could wait until they all stop falling or fell past a certain depth in the case one is falling forever. Then you fire the cleanup logic to animate the debris away before deleting them.
That may be a solution, depending on how large the wall is you may have to come up with tricks to optimize. That’s all for you to play with and decide.
It will certainly work and give you the effect you want.
Sounds like you have this to play with and some of your own research to do.
You should research UE4 destructable walls, and maybe slicing procedural meshes, or other methods.
Some other ideas for optimization. Maybe instead of the whole wall built out of destructible material, only portions of the wall are destructible and tie in to just standard wall assets, or there is a “finished” plating panel that can be destroyed to reveal the already damaged wall with chunks missing that was just hidden by the plate and revealed after it broke and fell off.