It looks like the universe itself will end anyway when all the expanding matter uses up its energy and contracts back down again to a single mass for the big bang to start again and I think its reasonable to say no intelligent life could ever survive that process so there is a finite limit to man's existence even if we reach the stars and even other galaxies.
Saying that I still think its important as a species to survive for as long as possible. I guess I have some loyalty regarding the human race for some reason and don't wish our culture to die. Just reading a book and engaging with the mind of someone who may not exist anymore is quite an amazing process when you think about it. When you look at the people of the past who have longed died was their existence pointless? I'd like to think it wasn't.
