The cabinet is cut into rough pieces, the wood more snapped in half than sliced. Harry cuts and cuts and cuts, until all that remains is a broken pile of useless rubble. Even then, though, it’s not enough. No, it could still be salvaged. Someone patient enough, someone stubborn enough, could still repair it; they could still puzzle the pieces back together and use it to rain destruction over the castle. Harry has the chance to stop it, so why wouldn’t he? He burns the rubble. He casts fire onto the planks and watches the flames grow until it all turns into ashes. Then, he vanishes the ashes.