I can easily see Cartagia as a Nero figure - very unpopular among the aristocracy, who don't see him as behaving 'properly' even before he turns out to be insane, but at the same time, his flamboyance and rejection of upper-class traditions endearing him to the common people - who, after all, aren't the ones being executed on a whim.

Hmm, now there's a fun idea for the direction Centauri facism/popular unrest could go in - revolts led by Pseudo-Cartagia figures. If nothing else, the suspicious nature of his death would certainly have led to conspiracy theories, and if he was popular, the idea that he wasn't really dead might flourish for a long time...