Everything we've seen so far indicates that Harry's going to be reinstated as the regional commander located in Chicago. Also, it's stated in the text that no one was willing to step into that position. I think it was in
Cold Case (just before Ramirez tells Molly he specifically rejected the job). Ramirez hasn't taken over Harry's job. He has been given the specific task of security for the White Council during the summit.
When Harry was regional commander, he mostly stayed in Chicago (basically acting as the warden of Chicago) and checked in on the wardens under him to see if they needed help. He occasionally went on missions. Kamp Kaboom and some stuff mentioned in the comic books were explicit. Other missions are implied. Harry only signed on with the condition he wouldn't abandon Chicago. Harry's going to stay centered in Chicago if for no other reason than to give Maggie stability. The Carpenters and her school are in Chicago. (I too would prefer if the story opened up to a broader scale, even if it's just so that his mom's gift isn't just shelved).
Ronald Ruel had enough time to be a noted artist. I know a lot of painters, sculptors, and such. That stuff takes up a lot of time even if you're just doing it semi-pro. I imagine Harry is going to have enough time on his hands that he is going to need to be doing some Chicago wardening. Having an ad in the yellow pages is a good way to do that. Murphy's also going to need something to do (if she doesn't die). She'd be able to handle a lot of the workload of routine detectiving. Harry finding lost wedding rings and such would be a good way to maintain an "officer friendly" reputation since the image we get of wardens, not to mention Winter Knight, is scary and unapproachable. And finally, Jim strongly implied that Faith Astor would be his client who kicks of the BAT.
https://www.reddit.com/r/dresdenfiles/comments/gbht7a/do_you_think_we_will_see_faith_astor_again_in_the/fp6ydqh/?context=8&depth=9. I mean, I assume he's a p.i. if he has an office.
S.I. may or may not be relevant for the rest of the series, but if you were the warden of/in a major metropolitan area, and you were on speaking terms with a division of the police force that was assigned all the weird stuff, why wouldn't you talk to them about keeping you in the loop? I doubt S.I. is too worried about the legalities of killing, how did Butters put it, "humanoid but definitely not human" problems. Most cops who know about the supernatural would probably be happy to let Harry deal with any warlocks too. You remember what old Jack Burton says, "cops got better things to do than get killed."
Sure, Harry is probably going to be kept busier by the BSF and the Paranet than by being a p.i. or something from S.I., but that doesn't mean he should ignore all other avenues of finding problems. Up to this point, somewhere around 15 of his adventures wouldn't have happened if he wasn't a wizard investigator for hire. I'm counting short stories. If we're talking just case files, it's 4-6.