I don't recall ever finding the Irish Air Corps hanging about the place any time I was out that way. I would be more than amazed if they got involved in plugging an ASW gap for the UK... the battle of the Atlantic in WW2, I would suggest, showed Ireland's opinion of helping the UK out during a life and death struggle, anyone banking on their assistance is barking.
Smiter is pretty well spot on. Herc and Merlin - anytime the cards are well and truly on the table this will be seen to be exactly what it is, 100% Bulls**t, unless the plan is to replace each Nimrod with 3 or 4 Hercs and a couple of dozen Merlin. The point is that to the vast majority of the general public, and not a few servicemen I would say, one aeroplane is pretty much as good as another - just as most people probably see nothing wrong sending something like a Scimitar in place of an MBT, or a frigate in place of a DDG. As long as the general public are so easily fooled why bother doing anything else? I bet we'd be pushed to fight the Belgians right now, if it came down to it...