I hate to suggest yet another GW2 option, but let folks join more than one guild.
Give guilds a filter option to hide inactive players by default so that way guilds feel less abandoned.
To compliment the above suggestion,
either A: have players with multiple characters in the same guild roll up under the highest ranked character they have and then have a drop down option to look/expand.
B: don’t add characters to a guild, add players. (this has some issues)