I wasn't here for the last one you were in, but that sounds challenging. I don't disagree by any means, having everyone in one guild would be pretty convenient.
There's also the possibility of multiple guilds who have worked together in the past. For example, if there had been a raid boss appearance. A group of X guilds would've teamed up and tried to take it on. Or even the fusion of other guilds into one larger guild, three individual guilds could do this to become a "Trinity" if I'm remembering correctly. Which could make it so that multiple guilds did exist, but upon the players consciousness transferring over we set plans to have them unite.
Just spitballing some other ideas. I was mainly asking because I started thinking about creating a guild, since that's a fairly important bit of info with the character in my opinion.