No, those are primary moral questions. Because the happiness of others is directly related to the wellbeing of the society as a whole and the stability and the wellbeing of the society as a whole is clearly the catalyst of our own wellbeing. Morality needn't be more complicated than that (though the term is loaded with religious bullshit).
In addition to that, we are programmed to care about others. This is a simple matter of nature. I have no interest to talk about exceptions or to discuss why our chemistry works the way it does, but the matter of fact is that most people care about their fellow human beings.
Again, this is simply in addition to the first point, which places our concern for our own wellbeing above that of others. We, are, as you say selfish beings. But we are also reasonable and intelligent beings.
As far as science not being able to tell us what is better. This is patently wrong. "Better" simply means better at producing our wellbeing and that of others. Any other argument relating somehow to some morality of the entire universe and/or unconscious matter is clearly ludicrous. Only people in funny hats need be concerned with the opinion of the universe, the rest of us can be content with providing a better society for ourselves.
Now, the question you propose is in reality very simple to answer within this framework of wellbeing for myself and others, like yourself. We both know that the extinction of the human race will not make ourselves or our children happier, or even existent for that matter. It is only when you attempt to think of morality as somehow applying to the entire universe where things become obtuse.
So again, within the framework of providing wellbeing for conscious beings (and we know our level of concern scales with the level of consciousness a being exhibits), these question simply become question like "Will destroying the entire human race be conductive of a happy society".
Well Mr. Slippery, now that I've thought about it, no, I think it will not.