I agree with this analysis; it can very well mean 'never' if one doesn't specify a time-frame and ends it there.Once again, لن يذهب is given the meaning as:
"He will never go" in the Urdu Arabic grammar book instead of the normal, "He will not go".
Both ways are acceptable, but the former is uncommon.The former is incorrect I think
this extends to all verbs. the differentiation always comes from the whole context of the sentence..the sentence لن يذهب simply means : (he) will not go, word for word ( future form)
لا يذهب means : he is not going now ( present form)
لم يذهب means : he did not go ( past form, but using the present tens verb)