I guess it is a "gameplay convenience" versus "role-playing realism" thing.
Well, I was always irrated that my NPCs actually had so few things to say to each other when they departed from one another, especially Mazzy and Valygar after their little fling.
I think one of the most logical things would be having them departed together, or arguing with PC about it, but from a player's perspective, it might be bad. In BG1, many NPCs were coming in pairs: Minsc and Dynaheir, Montaron and Xzar, and it was quite annoying; I myself had to kill Jaheira and Dynaheir more than once.
Also it would be nice to have some NPCs commenting after, for example Viconia gets kicked out, like "Good riddance" or "I'm glad she's gone, her presence lessened us all."
Again, in BG1 there were REACT_TO_DIE_SPECIFIC, i.e. if Tiax died, Quayle let out a witty one-liner; same with Jaheira and Khalid, Safana and Coran, etc. That, for some reason, annoyed me a lot. (Though I am all right with REACT_TO_DIE_GENERAL, if it is not something like "No sorrow for those lost in righteous battles.")
Some NPC could actually decide to write love letters to the PC, if they were once in a romance...or may be not.
"Dear Anomen,
I am fine. Well, Imoen has just gone crazy, I am slowly dying after having lost my soul, and Yoshimo... er, turned out he was a traitor, but it's okay, really. "
So, I think it would not work - for me, at least.