Guild Merger
There is no mechanic in the game for guild merging or changing the name of the guild. Whichever guild you want to keep (presumably the one that has the most improvements/influence) is where all the members go to. They could keep dual membership if there is they like to access the old guild’s storage, etc.
Sometimes in WvW, it’s nice to have a secondary guild people can go to and run incognito. Might keep the old guild for that too.
Personally I think far too many people start guilds, thinking they are going to do it “right”. Everybody and their uncle thinks they should not only be a member of a guild, but be a leader of a guild and that’s just silly. I guess you found out the hard way that it’s a pain for most people to lead a guild.
I started four guilds . . . . for storage. They are fully upgraded to 250 storage slots each. My fifth guild is the one I actually run with.
Have said person create(if not already created) the guild and invite those who want to join said guild to it.
Since each person can have 5 guilds it shouldn’t be an issue unless you’ve gone storage guild crazy.