The debate here seems to centre on whether the FO was right or wrong. It is rarely as simple as that.
It has been mentioned that the FO was quite inexperienced and it has also been suggested that the flight was 15 minutes from Derry. I'm not familiar with LDY but I know enough to know that the FO made a sensible decision not continuing to destination. That is not to say he would have been wrong to continue just that not to do so was a much better decision.
If he was over Blackpool or the Irish Sea arguing for a return all the way to Stn seems odd given the proximity of Dub, Man and Lpl not to mention Bhx, all of which are much closer with decent runways. However we dont know how inexperienced this FO was and he may not have been familiar with any of these fields. Also we don't know the actual condition of the skipper. If I was dying I would want my FO to get me to a hospital as quick as possible but if time wasn't critical I would be happy with a rookie taking their time and diverting to somewhere they were comfortable.
The bottom line is that the flight landed safely and all ended well. For that the FO deserves great praise.
It doesn't make his actions right however but merely appropriate given his experience. If an experienced FO did that and didn't dive into Man or somewhere close I'd lynch him.