An issue to consider is that by having players automatically leave their guild you could possible disband the entire guild by massacring a guild's membercount down to under five.
People are suggesting more and more options to influence guilds without needing to be the leader lately ... sure this might be more realistic but I think the people that made the suggestions don't always know how much time and effort goes into creating and maintaining a good guild. I'm not in the least worried about the guild creation fee but there are sacrifices and efforts put into guilds that go way beyond this fee.
I know that I wouldn't like it if my guild, for which I worked hard to get a background story up, recruited the right types of people and integrated it into the world of Yliakum, suddenly got disbanded or taken over by others. This would, without doubt ruin my gaming experience and possibly make me consider backing out of the game. This is still a game , keep in mind that it should be fun for everyone. Losing something you've put your sweat, tears and blood into is not fun for anyone.
These more realistic options, which make it possible to destroy or take over guilds are, in my opinion, going to be a source of frustration, grieving and intense conflict rather than a source of a more vivid gaming experience. I do know they're meant well, I'm just not convinced they'll be used well.