The climbing backwards departure you describe almost always means a lower take-off weight due to performance limitations, restricting the amount of fuel and/or pax that can be carried. Depending on local rules/regs, water landing may be an acceptable reject option in the event of a failure at a critical stage of flight (risking damage to the airframe if an engine quits at the wrong moment, but in theory not the pax and crew if the heli is equipped with emergency floats). This then enables the operator to use the clear area departure profile and utilise the full MTOW. Most (all?) S-76s have emergency pop-out floats within the wheel-wells