Jim Butcher hinted in an interview that Lasciel wasn't gone from Harry's life for good and I believe that she's hinted at again at the end of Ghost Story as the parasite which kept Harry's blood flowing. I hate to think that her shadow is still living in him; her sacrifice was so poignant. Rather, think how much torture Jim could put Harry through if Lasciel's coin were taken up by someone else (Molly... Thomas ...!).
(Also, I can really see Murphy with Shiro's sword (faith) and Thomas with Michael's sword (love) in the future. Re-reading the series, you see the word faith surrounding Murphy quite a bit - her faith in the law, in justice - and the same with Thomas and the word love.)