ToonTown Online was my after school life for over a year. It's been etched as a permanent memory as a wonderful experience. The kind of game at the perfect time, and that I would still love to lose hundreds of hours to.
As impossible as bringing back a dead MMO sounds, Disney actually finished the main story of the game well before shuttering it, and that has always stood out to me as a great reason to sell an offline version. Part of the charm was other people, but most of the charm was the Toons and the Cogs, and all of that needs to be preserved.