Of course, the automatic changing of leadership has its benefits as well. GMs may vanish for extremely good reasons, and this feature allows guilds to move on. Guildies are also protected from GMs who quit WoW without saying goodbye -- inconsiderate, but not evil.
I made the stupid mistake of parking guild leadership on a barely used alt once. I don't remember my reasoning. Seriously, why would I do that? So guild leadership got offered up, even though my main character kept logging in.
Is your GM taking advantage of the timing in a way that is detrimental to your guild? Or have you been in a guild where the leadership has been automatically taken from an absent GM? What were the results?