Played since classic and I have been in several guilds. As just a member/raider in these guilds, I never saw them die out. I left those for other reasons.
My only experience with a guild collapse was during wotlk where I was GM with several other cool ingame friends as officers. We started this guild very late BC so never got to raid then. In wotlk we started with nax and the other raids. Did fine in all tiers, but it started to collapse when ICC came out. We actually did OK progress. We killed the 4 first bosses fairly quickly.
The breakpoint came when we were working on one of the bosses. It was that ugly thing that spawned green shit on the sides and small adds that become big(cant recall name). Anyway, we had worked on him for some time and it was getting frustrating. Many faults etc. Suddenly, at one attempt we get him really low. It ended with a 1% wipe. After that, we never got close. Many of us got burned out so we kinda called it quits on raiding, but we kept on playing more casually.
This was a guild that mainly did 10 man. We tried during nax times to go into 25 man, but it got to frustrating.
Probably the best time I have had in wow. The raids we had was so fun. We were 10 people with various skilled players. Some were just your average gamer and some were really good. But all of us laughed on vent, talked alot and just had a great time. I will forever miss those days. All of those friends have now quit the game. All of them has come back to wow and random times between late wotlk and mop, but never stayed around.
I will forever miss the friends I made then and all the fun I had. Nothing can replace the special feeling I had during wotlk, where I was the GM of a guild with great people. It was not just about the gear and progress, but actually having fun with others. We were never the best, we knew that, but we had great fun.
Paranormal on Burning Blade EU. Best of times.
PS: This guild was sold sometime during Cata since my friend(who I gave GM status when I had a longe pause from the game) sold the guild for gold. He asked me if it was ok and I did not bother:P No one was around in the guild anymore, he had just used it for his alts.