There is one encounter with fishermen and mindflayer, can be missed.
You can miss it, and it's also possible to:
1. Walk away without doing anything.
2. Free the fishermen, then
walk away without doing anything.
3. Free the fishermen, talk to the mind flayer, resist its attempts at shmoozing you and... walk away without doing anything.
You can also kill it, of course. Or I suppose you could cast a healing spell on it, but even my most altruistic characters probably wouldn't bother.
IIRC, when the mind flayer is asked, "Who killed you?", the response is an image of a pod opening to reveal Tav's face.