An excellent contribution on the part of the Expanded Universe, in particular the Darth novels. The Sith played a very, very long game, secure in the ruthless efficiency of their chosen organizational structure.
And combined with the Old Republic's increasing and accelerating corruption and the Jedi Order's cocksure faith in its own powers and abilities to maintain peace and order within the galaxy that's why I think the Sith were destined to overpower and overthrow the Republic whether or not a "Chosen One" conceived by the midichlorians fell to the Dark Side and became one of the most powerful Sith Lords in history.
The Sith simply had too many tentacles in every corner of both the Republic and outlying powers and with or without the Clone Wars there would have been some catastrophic event or series of events that toppled the democratic order and placed a Sith Master on the throne of a totalitarian regime. Palpatine/Sidious and his series of apprentices just happened to have access to the greatest power and technology and the most cunning ideas with which to decay the Republic from within by turning it upon itself with the Separatist movement, the Clone Army and the resulting wars.