I always found it weird in MMOs when you are given a quest to save some NPCs, but you only save enough to get the quest done. A quest will say something like find a jailor's key and free (20) children. So, you kill the evil jailor. You find a bunch of cages with children in them. You start to free them. 3/20...7/20....12/20...18/20.....20 done!
Then you see another cage. There are more children in that cage! You go to unlock it. You can't. Quest is done, so screw those little brats.
I just always found that odd. Seems to me, if you have a quest like that, you should be able to keep freeing them if ya want, or all the children get freed when the quest is over.
This would required phasing, but it would have a more real feel to it.