Maybe it's an insane anal internal struggle, but for me, a little part of me feels pain when someone decides to move on from my WoW Guild. I know there are so many reasons under the sun that have nothing to do with me for moving on, quitting the game, or whatever the case may be, but you can't help think that perhaps it was a personal failure on your part when someone decides the guild isn't for them. Did you not raid enough? Did you raid too much? Was it someone else that annoyed them and you didn't respond quickly enough.
Well, what do you do? If you are a "social" as the Greedy Goblin would call you, then you want to be liked. I think this is totally the wrong approach. You have to be somewhat detached and remember these are all perfect strangers and they will all do whatever is in their own best interest. This game encourages selfishness....
"what have you done for me lately"?
So, yes, you have a job as guild leader and that is to provide them the thing that makes them stay so long as it fits within the confines of your definition of how the guild should work. It may seem to you that I am trying to convince myself of these philosophy and you'd be half right.
As much as you logically know this is how things are and how they should be, you can't help being human and having feelings.