Well in any case they probably just died from isolation then since they can't travel reliably and they aren't the craftiest of folk. But then again perhaps Ireland turned into like some giant wild island filled with tribal warfare then, that makes sense.
We aren't the craftiest folk?
Ever heard of Yeats or Joyce? Two Irishmen recognised as arguably the greatest poet and writer of all time respectively. Or Shaw, Heaney or Beckett? Three Nobel Prize winners.
How about the physicists Tyndall or Dalton?
If you want to talk about craftiness particularly, how about the Irish Republican Army who in the 1920s, fought the most powerful Empire in existence to a stalemate, and did the same again to an admittedly weaker Britain in the 70s, 80s and 90s?
You're talking about us being dumb and you probably have either "Yes we can" or a confederate flag on the back of your pickup truck.