Nothing Matters - that was Freddy Mercury in Bohemian Rhapsody - nothing really matters to me.
Ron, you said "We cannot imagine a universe in which we are not present", and then you followed that up by saying "You cannot, therefore, imagine a world where you aren't in existence", and now the seemingly contrary statement "I did not say that it is impossibkle to imagine a universe without human life".
You seem, as far as I can tell, to be applying a novel concept of time here, whereby all moments exist in an eternal present. It reminds me of Castaneda's theory of the nagual, that we are surrounded by eternity. By some interpretations of that view, the past and future are present in the world. Heidegger explained the presence of the past as facticity, and the projection upon the nothingness of the future as existentiality.
The past no longer exists, and the future does not yet exist. In the past, humans were not present in the universe, and if we go extinct, humans will not be present in the future. Ergo, it most certainly is possible to imagine a world where humans do not exist and a universe in which we are not present, unless we redefine words to say the past and future are present.
Bob Dylan put it even better than Freddy Mercury, "for the present now will later be past". But then, I suppose nothing is eternal.
Difficult as it may be to imagine non-existence, it is also hard to imagine reading about nothing for 248 pages. I suppose there is worse - in the seventh circle of hell David Letterman talks about nothing for ever.