I could think of battling Umlaut in a new mode I know from several other games as kind of World Boss, which would mean Umlaut having a ridiculous amount of LP and this fight needing to be tackled by all members of the guild together in order to take him down. Should happen once a week, I suppose best on a weekend where most players have time to join the battle, and that fight running for 24h, every member of the guild being able to do 3 attacks on him. Umlauts LP amount should be based on an educated guess of the average damage ability of the guilds members, making it possible to overcome him if at least 80% of all members take part in that battle and do their 3 attacks on him.
Would raise guild team-work attitude and be quite fun to make this big achievement together.
And it wouldn't have to be the end of the story, since it could be said to be an attack from Umlaut on the guild, since its continued efforts to free his captives and take him down raised his attention and he found it necessary to counter those. Would leave everything open for the final showdown in the story, as a victory would only mean successfully having defended against his counterattack, but not at all having overcome that big ugly (he surely must be, how can someone so evil and mean look good?) curse making the Dragon World (btw, has it got a name at all?) such a troubled place currently.