As AlexanderWales says, the biggest flaw is the wand. If you add a line about harry being left holding his wand so that Voldemort can impose further unbreakable vows if he sees fit, or he has it left in case he needs to demonstrate any secret knowledge (along the lines of Patronus 2.0), Voldemort goes from holding the Idiot Ball to just making a mistake. He's trading off Harry possibly doing something impossible with his wand vs a far likelier benefit.