JB, having floats and lifejackets is not about eliminating accidents but reducing the risk of death or injury to persons.
Here Here.
Having had mechanical issues in twins that required immediate landing, namely; one at night in the country, one at night over a city with a river, and the other over Southbank in London in daytime, it is a good idea to wear a life jacket if regardless of the number of engines, a significant part of the flight relies on ditching as the primary emergency landing site.
JB, perhaps if floats were available and had been deployed and even if the aircraft had ended up inverted but floating, it would have been easier to rescue the trapped passenger? Also if it is floating upside down there would be filtered daylight in the cabin which would aid self escape. The alternative of sinking into a state of near darkness makes for an immensely challenging escape to say the least.
Even if you do get out there is still the risk of hyperventilation, however it can be mitigated by a life jacket, especially one with a collar that supports the head and rolls the wearer upright.
I witnessed, at close hand, three people capsize a small row boat in very cold water and one of them hyperventalated which is a shocking sight, surprisingly violent and there is little hope if you can't keep your head out of the water because you continue to suck and pant uncontrollably even when your head is under the water.
In this case his (auto inflation) life jacket saved him by keeping his airway out of the water.
I took a HUET course after witnessing that and dont complain about immersion suits as they greatly reduce cold shock and hyperventilation.
Interestingly the guys who did not hyperventilate were rescued first as they swam to nearby boats which unfortunately blocked their path to the victim who needed the most urgent help.
Mickjoebill