I could be wrong but, even if Wikipedia says his departure from the company happened late into the game production, I recall reading that Jim already had a foot out of the door at the very beginning of the game production. I think he provided general ideas and guidelines at the start but was not present during a big chunk of the production and the game was mostly designed and written by Mark Crowe and Jane Jensen as a result. I don't think Jim had plans for a fourth game. If anything, it's probably Mark or Jane who left that door open in case Sierra wanted something to build a potential sequel from. I do recall that he had plans for a follow up to Blue Force however but that just didn't happen.
I'm not a big fan of the third game myself. It's okay but it's nowhere as good as the first two games, it lacks the whimsy charm that Walls put in the previous games, and plot wise it feels like a patchwork of all the gritty Hollywood crime stories tropes at that time.
I'm fairly sure Sierra still had the rights to Sonny Bonds and its characters, but Darryl F Gates didn't like the previous games, found them too focused on Hollywood type of stories and just wanted to tell a story of his own and give his vision of police work rather than follow up somebody else's story and vision.
Post edited November 22, 2016 by blueskirt42