Okay, I get it now. Must be too early in the morning for me. 
As to the timing of the keeper refuting the chance of it being Londo's greatest fear, very good catch. That's part of the trouble with time-related plot development. It can be forgotten all too easily. Your argument would seem to remove the keeper from the list of candidates, leaving Londo's death at G'Kar's hands as the most viable choice. I say that because arguments against it seem to be less solid

As to the timing of the keeper refuting the chance of it being Londo's greatest fear, very good catch. That's part of the trouble with time-related plot development. It can be forgotten all too easily. Your argument would seem to remove the keeper from the list of candidates, leaving Londo's death at G'Kar's hands as the most viable choice. I say that because arguments against it seem to be less solid