Practically, le`olam in negative constructions is "never". Cf. the very similar statement in 2:14ff:
The wise have eyes in their head,
but fools walk in darkness.
Yet I perceived that the same fate befalls all of them.
Then I said to myself, "What happens to the fool will happen to me also; why then have I been so very wise?" And I said to myself that this also is vanity. For neither the wise nor the fool will ever (le`olam) be remembered, as in the days to come all will have been forgotten.How can the wise die just like fools?
Postulating an "age to come" where everyone would be remembered (as in post-Pharisaic Judaism) is as far as one can get from Qoheleth's thought. This may be the only way to understand Qoheleth from a Pharisaic or Christian perspective, but it actually ruins the original line of reasoning. For if such a future age of retribution is to be taken into account, then it cannot be said anymore that "the same fate befalls all" etc.