Before you can expand on this you'll need to rewrite it as everything's already happened. Well except for the killing of the Death Eaters that is. And they do have to go!
If not they'll simply await next idiot to decalre him or herself the Dark Lord/ Dark Lady and the whole stupidity starts again. However, Harry should claim ALL their assets as spoils of war. Leave them so broke they can't even pay attention. This is a good story and I wouldn't mind if you expanded on it. But that is entirely up to you as the author.