Lasciel can't be gone for good, because, well, that would suck.

As for Harry cleaning up Chicago... well, since he's been gone it's basically been the Fomor (and probably some randoms) vs. The Better Future Society, which is Marcone, the White Court, and Harry's old buddies.

Even if it's a case of pitting baddy against baddy, it doesn't really seem in Harry's character to let Chicago be dependent upon Marcone and succubi for protection. Also, we've done a bunch of "cosmic" stuff in the last few books, something more local wouldn't surprise me.

"Peace Talks," I think I just got the name from Butcher's Twitter feed, or something. No idea what the plot would be.