Given the right conditions there is indeed a slight chance of post-crash survival. There was the woman who survived the crash off the African coast. The Potomac crash is another case of a successful ditching.
Jimlad is correct in stating that the probability of a ditching is vanishingly small and that the cost of maintaining a long range search capability is huge. The answer therefore appears to be one of cost-benefit economics.
The military task (trails) is not what it was; the civilian risk is low; the value of a human life therefore is deemed less than the cost of maintaining SAR cover.
The prime purpose of the fixed-wing SAR platform was search. The prime purpose of the RW platform was rescue. We could then make a similar argument to disband the military RW SAR role for the same reasons.
Oh, we are
