If you want a slot to record which actors were destroyed in that level, it will reset if you overwrite with data from another level.
You can either create 1 slot per level or keep a list of dead actors yourself in game instance with soft references to those actors and save/load game instance. If an actor is in that list after load then just destroy or hide it.
Yes structures and struct blueprints are safely supported unless are doing crazy things there, like having a deep chain of nested arrays of structs with arrays of object pointers with more array of structs and so on.