The AOPA guys did a study on the survivability of ditching. I don't have the exact number but I recall that 90 + % resulted in all surviving the ditching and exiting the aircraft. Survivability after the ditching was obviously heavily dependent on how close help was and whether or not the pilot/pax were wearing life jackets.
My home airport is on a spit with water adjacent to one end and about a mile off the other end. If it is busy it is not unusual to be out of gliding distance of land while in the circuit. For that reason and the fact that there is a lot of other water nearby, I always were a constant wear type horse collar style life vest on
every flight in a SEP.
I also fly sea planes and the survival numbers are much lower because of the sudden unexpected and usually violent upsets that occur when control is lost on the water. Here the survival numbers are much worse, with typically people drowning inside the aircraft before they can get out.
A egress course is IMO an absolute must if you are flying or even in a seaplane. As a very experienced scuba diver plus a regular breath hold diver I thought it would be a piece of cake. How wrong I was
This training provider had a mock up of a small light aircraft trainer cabin. You were strapped in then they submerged it gave you a good shake and shuffle and left you upside down. The first time I ended up totally disoriented and was never able to escape, instead the safety crew had to raise the cabin above the water. I tried it 6 more times include blindfolded and by the end was secure in the knowledge I could escape pretty much no matter what happened.
However if that first time had been a real crash I would probably not be writing this..........
Finally you can only escape an crashed aircraft in the water or on land if you are conscious. The No 1 way to ensure you stay conscious after the crash is to have and wear a shoulder harness. I will not fly in any aircraft that is not fitted with one.