Actually, by far the most implausible thing we’ve seen the tadpole do to my mind is save us from the fall from the nautiloid. It doesn’t make a lot of sense to me that it would protect us from that and not from dying in myriad other ways. (Unless we were actually caught in some area safety effect of the nautiloid and it wasn’t the tadpole at all!)
I saw a theory somewhere that we were saved by Kelemvor's interference here. It was all explained through Wither's hints when talking to the cleric of specific deities and some other references. I don't quite remember now, sadly, but it was quite convincing.
