Sikozu was not originally meant to be the spy. It was going to be Noranti, but the actress was having issues with the makeup, so they reduced her role in PKW. If you look, there are actually two different actresses playing Noranti throughout the movie.
As for the comics, no, I don't think they resurrect D'Argo. I think the D'Argo comics actually take place before he dies in PKW. There are other comics that are a continuation of the series, and they're actually very well done. The art is great, and the characterization is perfect. Unfortunately, the comic series was just recently discontinued.