I have seen a few studies on ditchings - albiet mostly conducted in the US. These suggest that survival rates are much higher than you might anticipate. For example in a ten year period based on just over 200 reports the survival rate was a little over 90%.
However as with any stats. a proper understanding can only follow from the ability to correctly interpret the data. There are many obvious factors which will impact on surviving a ditching; in particular in and around the UK the temperature of the water and the speed with which the crew are recovered is critical. Needless to say so is the ability to exit the aircraft as the evidence indicates most GA types sink quickly. The fitness, size and weight of the crew are factors and in this case so is the design of the aircraft.
Never the less I think it is safe to conclude the risk of an engine failure followed by a ditching that results in loss of life is an very rare occurence so in terms of am I likely to die in that way, the answer is you are not.
Categorically without reference to this accident, the vast majority of accidents are down to human failure in some way. Theoretically a twin is always safer than a single, but the theory is substantially eroded because of the high rate at which pilots mismanage twin aircraft - be it running out of fuel because they dont fully understand the more complicated fuel systems on some twins to botched EFATOs.
Once again this makes any comparison meaningless unless the reader has a propoer understanding of the factors involved.
Ask the question how safe is flying (over water, at night, in IMC or whatever permutation you wish) and the answer should be caveated with how current and well trained is the pilot, how careful has the pilot been with regards to the maintenance of his aircraft and what precautions has he taken to stack the odds in his favour? If the answers are all weighted in the pilots favour then inevitably you will be much safer in a twin than a single, but in both instance the risk is so small that some would argue it hardly warrants concern - you would do far better eliminating other risks in your life such as having a annual screen for cancer - very few of us do but statistically there is a far greater chance that will kill you.
In reality it seems to me most peoples perception of risk when it comes to flying (and lots of other things) is qualitative, or should I say emotional. We think about the risk of a flight over water, but we dont think about the risk of cancer or hypertension being good examples. If we did and applied the same criteria I have little doubt we would all have far more regular health screens and we would all approach flying (never mind flying over water) in a different way. In reality we often debate the risk of flying over water in a single but we never ask why we dont have annual health checks.