I simply pointed out that the question asked - what would happen is someone (or everyone?) was convinced their moral beliefs were wrong - was vague in several important aspects.

It's vague in an additional way: you interpreted it to mean "what would you do if you were convinced that your moral beliefs were wrong". But I think Eliezer was asking "what would you do if your moral beliefs actually were wrong and you were aware of that."

That has its own problem. It's like asking "if someone could prove that creationism was true and evolution isn't, would you agree that scientists are closed-minded in rejecting it?" A hypothetical world in which creationism was true wouldn't be exactly like our own except that it contains a piece of paper with a proof of creationism written down on it. In a world where creationism really was true, scientists would either have figured it out, or would have not figured it out but would be a lot more clueless than actual-world scientists. Likewise, a world where moral beliefs were all wrong would be very unlike our world, if indeed it's a coherent concept at all--it would not be a world that is exactly like this one with the exception that I am now in possession of a proof.