Shawn
Sounds good in theory but maybe you haven't seen a decent N Sea sea state close up and personal! There are various reasons not to:
1) The rotor blades are likely to chop the liferaft and its occupants up (and if you keep collective pitch on to reduce the liklihood of that, the downwash will have the liferafts everywhere except where the pax can board them dry)
2) After you happily taxy off into the sunset, what are you going to do when you find that all the pax are in the liferafts without crew members to lead them, and you are left with no rafts!
If its OK to shut down and then get into the crew liferaft (if there was one), surely its better to all do it at the same time. Or do you think that the captain should go down with his ship to save the women and children who might be on board? The difficulty with that is the cockpit of an S Puma or 92 is not tall enough to stand up and salute whilst the water comes over one's head, therefore rather spoiling the effect.
In reality, most of the time a big heli will float right ways up after shutdown, even though the motion will feel dreadful to the crew. If its that wild, chances are the liferaft will go upside down from time to time too. As we have said before, surely its better not to end up in the water in the first place, and for that we need good design, not paper safety.
HC