That article is a good presentation of the facts.
If you are trying to be extremely risk averse then go Mull of Kintyre across to Fair Head. Its something like 6 minutes flying time with no airspace above you so you can always be within gliding distance of land (of most planes).
Survival time in the Irish sea without a life raft is estimated at 1 1/2hrs. Life rafts would prolong that but that assumes you are able to operate it and get into it - easier said than done (I've done the training for operating passenger ships).
If word gets out that you are in trouble (you get through on the radio), your PLB works and you ditch successfully (and the stats are actually quite good with ditching) then you should find a helicopter above you well within that time. If one of those bits fail, things become more difficult unless you have a raft you can get in to.
Would the pilot be irresponsible for having made the decision in the first
place?
I would say only if they were un-prepared (no life jackets) or were flying in conditions that weren't suitable.
However - this is an internet forum so someone would have a bitch...