Is it the Underdark that you are talking about or NPC quests? NPC will leave your party after you ignore their requests after a while (usually they warn you first).
In the underdark, there are time limits, so listen to the princess's every command or else you'll get CAUGHT and end up fighting a entire drow city!
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Greetings Mortals. My Name Is Wah, Arch Lich Wah.