I don't think the Xander-Cordy relationship needed any closing, the way its being discussed here. It was a typical high school relationship; those types of things never last, and people grow out of their high school experiences quickly. To speak of myself, I don't feel a need to go back to high school of all things and find "closure" because what I was back then I grew out of and left behind a long time ago, which I think is typical of most people's life experience. High school relationships are usually nothing worth dwelling on when viewed with distance and posterity, and Xander and Cordy are no different in that respect. There is nothing back there that needs tying up for either character. Also, Cordy especially moved on and far past it by the time any crossover into Angel would have made sense. Cordy didn't need closure at all; in fact, she left him behind with all of the rest of her high school companions and memories.