From what I've read, Francis II abdicated for worry that Napoleon would take the title for himself, but could Nappy really do that?
Wouldn't Nappy have to wait until the Francis died and seeing as how Ferdinand (Francis's heir) was challenged/prone to seizures and epilepsy it'd make sense that no elector would sensibly vote for him and may have to by obligations vote for Nappy. Could Nappy have taken the Imperial title from Francis in a peace treaty (I doubt that'd be recognised though)