In the original Ravenloft module (back in 1st edition), the encounter with him was one that was far creepier than dangerous. Essentially, Strahd kept this guy captive for "longer than he could remember" and chained to a desk so that he could keep track of Strahd's monies and activities. The catch, however, was the fact that Strahd did not tell him about most of the money he had, and Leif knew it. Not only was this guy being held captive and kept alive for far too long, but he was deliberately teased with mere possibilities of performing something as simple as his occupation.
It was not a physically threatening encounter at all; only one to help build the paranoia and creepiness of the module. Anyone could have killed him without effort, but if the PCs killed haphazardly through the whole module, there was no way to get out alive. Certainly a classic module.