As a piece of performance art, the stunt wouldn't have as much impact if it was shredded during the auction. The idea of establishing a classical 'value' of an object by process of auction only for that object to be classically devalued moments later allows you to explore what gave that thing its value in the first place and what takes away its value after its 'destruction'. Without having a clear moment of delineation between these two states, you don't have a clear way to discuss and understand this question.