Riding it all the way down, baby!
The Escapist recently published an interesting article called "Riding the Failure Cascade" which examines how a few individuals leaving a volunteer group will often spark a spiraling chain reaction that can destroy even the largest of organizations, with a look at EVE Online as an example.
Guilds are really just volunteer organizations, and consequently, they suffer from a lot of the same problems. Guild leaders function as coordinators and morale officers as much as they do running the group, because volunteers are easier to lose than they are to come by. And once a guild begins to lose a steady trickle of members, it's only a matter of time before that trickle turns into a full-on waterfall. This phenomenon is called the "failure cascade."
Keep reading at The Escapist.