Loyalty and dedication are very important, but i think the keystones are above everything else. Of course a clan needs stable leadership, that makes smart decisions, but the true heart of the clan lies within those few core members that your clan can't do without. These members aren't necessarily ranks, but very experienced members who are looked up to, and just bring the clan together. Without these members, or when too many of these members retire, it can cause a decrease in morale in a clan, and possibly cause the clan to close.