Regarding comms, I've had no difficulty 'coasting in' with London Information, sometimes at low level like 1500', in the area where this tragedy apparently occurred.
The comments that I and others have contributed about poor radio coverage in the Irish Sea relate to the area off Holyhead, possibly because Snowdon shadows the Clee Hill transmitter.
However, this aircraft was apparently inbound to Cardiff and it can be very difficult to raise Cardiff until very close in when following the S Wales coast at low level, presumably again because of terrain shadowing.
Writing as one who uses this route several times each year, it is heartening that the response from Cardiff and D&D was such that if these poor people had survived in or on the water, they would have been picked up.
Sincere sympathies to all those involved.