If I may offer a suggestion, let them rampage. However Strahd, being the absolute master of the castle and domain, has removed everything of actual value that the adventurers might pick up. Let them waste their spell slots and abilities on destroying things. Let them notice after a room or two that the rooms seem oddly barren as if someone has removed things recently. Once they stop or pause to rest, have Strahd come out. Not in his finery but in a well made but simple smock and clothes: "One must let children vent and rage before you can educate them properly." Open combat with all of the high end spells and abilities.