Having a durable, long-lasting guild is a difficult chore in the world of Warcraft. Attachments are often virtual, play schedules vary, not to mention the extremely broad codeword "drama". If you want this goal though, the only way to achieve it is to anchor the guild around your core membership. What is your core? It's the people you can depend on, those who play often, get involved in operations, maintain a positive attitude, demonstrate some skill, and keep plugging on during good times and bad. If you're in charge of or can shape the guild, those are the people to keep in mind when implementing policy and making arrangements. New members might become core, or they might leave. Long-term but unreliable members won't be there for you. Certain things, especially loot and formation rules, should be fair towards everyone, guilds that operate as pyramid schemes don't last. But if you match your core's interests to what the guild is doing and how it operates, then it has the greatest chance of longevity.
Luckily I've almost entirely been in the same guild for the bulk of my WoW career, roughly 3 years. While its direction sometimes changes, in general it holds to those principles, whether directly or indirectly. I was an officer for a large chunk of that time, and in that position I've learned over time that when the chips are down, you have to keep things in line with your chief membership, it's the only way to keep the ship sailing.
3 days ago