Inputshaft
that redundant - TSB reported a power interuption to the FDR, just before the very non redundant tail rotor take off failed.
Sox6
The structure of the checklist buries the actions associated with this failure deep within the checklist.
You are correct there is no warning or clear criteria prior to needing to ditch, especially in light of the late 2008 Sikorsky Safety Advisory that was written to stop ditchings due to vespel spline failures that could cause the oil pressure to drop from 55 psi to just about 7 psi and caused 3 prior emergency landings (1 x Norway, 2 x Brunei).