He said in a letter to emcee Jamy Ian Swiss, published on his website, that his health prevented him from attending the May conference:
Please convey my thanks to the entire Executive Committee for their gracious apology and for reinviting me to the NECSS conference. I am sensitive to what a difficult thing it must have been to rescind an earlier, publicised decision. I am truly grateful. Politicians are regularly criticised for changing their minds, but sceptics, rationalists and scientists know that there are occasions when the ability to change ones mind is a virtue. Sympathy for the victim of a medical emergency is not one of those occasions, and I therefore note with especial admiration that the Executive Committee’s courageous and principled change of mind predated my stroke.
That stroke, however, does make it impossible for me to accept the invitation, much as I would like to do so. I shall especially miss the pleasure of an on stage conversation with you. I hope another opportunity for that conversation will arise. I wish the conference well. May it be a great success. You certainly have managed to put together a starry list of speakers.
With my best wishes to you and the whole Executive Committee
That’s a hell of a classy thing to write given how he had been treated.
NECSS, as far as I can tell, still plans to hold a panel discussion to talk about Dawkins’ comments. No word yet on who will be speaking on it.