A school that saw part of its main building collapse last January and its students shuttled to other campuses for a while is whole again. For the first time tomorrow, all of Summit Country Day School's eleven-hundred students will return to the campus in Hyde Park. Last winter, construction workers renovating the private Catholic school dug out too much of the building's foundation. A 30-foot portion of the rear wing collapsed. No one was hurt. But repairs were necessary and some students went elsewhere until the end of last school year. The construction was for an eleven million-dollar expansion that was unveiled to parents Friday. The new Lower School has wireless Internet access, three playgrounds -- including one on its roof -- an art room, gymnasium and two fireplaces in its libraries.