Kordac: The way to get shot of one character without losing their partner is quite simple.
Find a building you'll never enter again then take control of the character you want to ditch and enter the building and close the door while leaving the rest of the group outside.
Once inside remove the unwanted party member and because they can't reach your character to complain (NPCs can't open doors on their own) their partner doesn't take offence and leave.
LoL, that's bloody game breaking*.
Getting one of your companion killed is more akin within RP perspective, because you know from the that kicking one would meaning loosing two...