Harry's going to stay in Winter through at least, the next two books.
BG ended right after midsummer. Mab, Molly and Kringle visited Harry on Christmas Eve. Obviously, Harry is still in Winter 5-6 months after BG. Which means he missed the Halloween window to change masks. Twelve Months takes place from June-ish to June-ish. If Jim keeps pace, Mirror Mirror will take place about a year later, giving one more Window for Halloween swap. Since Mirror Mirror's focus will be on Harry for a change, something we haven't seen since Ghost Story, I expect revelations about Starborns in there. Winter will be playing a supporting role. Probably still complicating Harry's life, as normal.