I’d further say that typical party structure is not necessary for an emergent story to be created and the play be enjoyable.

I agree in principle that character co-operation is not required for an emergent story. However, my preference and experience is that it is typically important for most players in an ongoing campaign. If characters can’t find some common ground, what reason do they have to continue to associate in the manner typical of PC groups? Additionally, a character whose representation is such that it either forces other players to “misrepresent” their own characters (i.e., continue to associate with a character they normally would not) or stop associating with that character is not fair to the other players nor do I find it generally conducive to an ongoing campaign. This is why I prefer a certain level of collaboration at both a character and player level in my campaigns (with, I hope, a healthy level of player character conflict as well).

Representation has to be tempered by the fact that the game and, hopefully, the emerging story are a collaborative effort amongst all of the players. Having a character who will not fit in well with the rest of the group will not work from a representation and collaborative approach (that’s probably a topic for another post though).

I, too, like to create emergent stories when gaming. I do not find it necessary for all player characters to form a party of any kind; the characters may actively try to slay each other for all I care, as long as the players are co-operating.