WolfishMusings,
It seems that your question has been answered in pieces throughout the posts above.
Statement 1: We are obligated to try and stop a Jew from sinning.
Statement 2: An ain ma’alin who falls into a river is not committing a sin, therefore to not bring him up causes no conflict with statement 1.
Statement 3: Suicide is a grave sin.
Statement 4: See statement 1.
Do you disagree with any of this?