This is actually an interesting concept. Similar to Skyrim, where there are mercenaries in taverns, it could be neat to have randomly generated player characters, as in randomly picked from the pool of characters that are offline, to be wandering around the world. Some in taverns or banks, some walking the roads or injured by the side of a dungeon, and if you help them or pay them, they'll become a temporary companion a la the companion system, except they only last until you log out or dismiss them, or someone logs onto that character at which point the NPC says that they have other things they have to attend to and walk off. I think it would be neat. It'd never happen, but it would be cool.