Complex sentence: Young men and women were either lowered into these wells and left to drown there so as to make them enter the realm of the rain deities, or were only thrown into the well later to be drawn up again, and give oracles.
Split into simpler sentences: Young men and women were owered into these wells and left to drown there, so as to make them enter the realm of the rain deities. Alternatively, they were only thrown into the wells later to be drawn up again, and give oracles.