After Zarmenon’s assassination (which was provoked by his own plans to assassinate certain members of the party) and Vorn’s execution (due to being both too dangerous and too crazy for even other Drow to trust), we agreed as a group to refrain from PvP, because of decreased play experience as a whole. Both of these incidents had been preceded by Ibari’s assassination (triggered by Identify “embezzlement”).
While this could be considered “metagaming”, especially in a group composed (at the time) of almost exclusively evil-aligned Drow, we decided that in this one case the “Game” came before the “Role-playing”.
The agreement worked out well and I believe we all enjoyed the game much more after that (we had more than enough powerful NPCs trying to kill us or worse without having to worry about party members doing it too :p)
(Mike also later specified that if we/he wanted a specifically PvP game he would have structured the game’s time scope and starting levels differently to facilitate that.)