Unfortunately, at least here in the U.S., the entire section requires replacing. Problem is, they come assembled from the factory and most glaziers aren't set up to replace, seal and refill with argon. Before you go to the expense of replacing the window and if you can live with the crack, wait until a cold day and see if the affected section gathers moisture on the inside between the two seperate glass pieces. If so, it'll have to be replaced since the inert gas has escaped and there's little if any insulation properties left. If it doesn't sweat, it may be the crack is still sealed and will wait until spring, if you choose...