Napoleon contemplated fully dismantling Prussia in 1807. Had he done so and still managed to lose down the line (likely with Austria and Russia playing a larger role), what would the Concert of Europe have looked like?
Napoleon's 1807 plan involved giving Silesia to Austria and I doubt the Austrians would want to give it up.
Russia may get Posen here.
I image there'd be some kind of Prussian restoration, but certainly not one that involves Austria giving up Silesia. Maybe Prussia gets Saxony?
There'd still be a desire for there to be a watchdog in western Germany against France. The two most likely prospects, I think, would be a Rhenish Kingdom (potentially including Luxembourg) or a greater United Kingdom of the Netherlands that satisfies all of the desires of King William (North Rhineland and connection to Orange-Nassau). Alternatively, restored Saxo-Prussia just gets the Rhineland.