Back to the topic:   It seems that those atheists who may try to claim that Darwin was atheist but did not declare his atheism due to concern for his wife need to come up with some evidence.

It appears that he was never an atheist--from his own personal conviction above all else.

Wikipedia is not of course infallible but on this topic it quotes Darwin--, late in life, 1881, after he had finally rejected Christianity-- in a meeting with an atheist who sought his support:

Darwin:   Why do you call yourselves Atheists?

Guests:    We did not commit the folly of god-denial (and) avoided with equal care the folly of god-assertion.

So Darwin pointed out that what they were describing was agnosticism, not atheism.

Darwin:   I am with you in thought but should prefer the word Agnostic to the word Atheist.

Darwin was in fact by the end of his life an agnostic--but never an atheist.

It is also not reasonable to speculate that he would have become an atheist had he lived much longer.   The Dow Jones average went down 82 points yesterday. At that rate in 100 days it will be below zero.   Extrapolation of a trend into the future is groundless--and senseless.

In fact it makes eminent sense for a man who relied on empirical evidence in his thought to reject fundamentalist Christianity--but also reject atheism--since belief is a field in which there can obviously be no conclusive proof.