I know the whole blog is tagged as non-spoiler safe space, and sanil is busy with school so the chances of her seeing this and reading it are slim, but I can't remember how far into the series she's read, so I WARN.
DON'T READ BEYOND THIS IF YOU HAVEN'T READ EVERYTHING CURRENTLY PUBLISHED AND/OR DON'T WANT TO KNOW SOME OF THE TIDBITS WE'VE LEARNED ABOUT GHOST STORY!
I MEAN IT!
I AM NOT RESPONSIBLE FOR ANYTHING BEYOND THIS POINT!
Right then. So, in WoJ notes, we learn that the runes/sigils/markings on the lighthouse/keepers house on Demonreach that we see in Turn Coat are related to/the same as some from the Welcome to the Jungle comic. The only ones I can think of that Harry doesn't use himself are the ones that the Hecatean was using on her file cabinet. Those, which Harry knows enough about to understand what they're fore are described as being preservative. Making the cabinet a magical fridge, sort of kind of.
Harry spends most of a year dead, and then comes back at the end of Ghost Story. Demonreach is at the end of Ghost Story. Somehow, Harry's body is preserved well enough that his soul/spirit can be put back in it and not be all icky and zombie-esque.
So. Harry's body is being stored in the keeper's house on Demonreach. Mab is also keeping all of Chicago really freaking cold, to help things along, but the magic on the house is doing most of the job.