As someone wrote in an earlier post, the crux of this (I suspect) is the apparent absence of a Plan B/C for the intended flight. Diverting to Valley and getting a taxi to Holyhead and a ferry across to Dublin is an obvious Plan B but had this been discussed and was there time left before the Christening? Turning back and getting a Ryanair/Easy flight to Dublin was also a valid alternate plan.
It seems outrageous but 5 people have died because the weather over the Welsh mountains was a lot worse than the weather around Milton Keynes and nobody had anticipated it.
What an absolute tragedy.