Bonapartism is an inherently unsustainable regime type. From a Weberian perspective, it stakes its legitimacy on the charismatic authority of an individual leader, so it can't outlive its founding leader the way a regime staked on bureaucratic-rational or traditional authority can.
Agreed. Which is why I think, had the Bonapartes actually made their dynasty stick for more than a generation, their regime would have had to convert itself eventually into something rather "un-Bonapartist." Most likely, a fairly conventional constitutional democracy, which is what Napoleon III's regime was steadily transforming itself into when Otto von Bismarck so rudely interrupted things. Because the odds are you can't get a dynast who is highly charismatic and capable - not even to Napoleon III's level, let alone Boney's - in every generation.