at this stage in his life it makes sense for Sonny to go legit. He has legit businesses, and frankly the mob boss stuff has been old for quite some time. To move Sonny out of that life and giving Maurice something different to do wouldn't be a bad thing.
Besides, just because he's no longer a mob boss, doesn't mean that previous work relationships can come into play if the show wants to revisit the drama of the shady side of his life. Plus there might be some solid story for Sonny as he tries to get out of the business, and I think the main thing long-term characters like is a storyline that takes them in a different direction instead of variations of the same story.
Karen L.
