I think a copyright case would be very difficult for WotC. The game rules and algorithms, themselves, are not subject to copyright; copyright only applies to the presentation of those rules. OSRIC is written from scratch (i.e. an original presentation), and it uses the OGL, which means it has permission to use terms that might otherwise be considered part of the "artistic presentation" of the game algorithms and rules (e.g. hit points, armor class, class names, spell names, et cetera). It's really the OGL that makes OSRIC possible, IMO.