Atheism is just the other end of the stick of religion. But at least Atheism is not as contradictory as most other religions since it does not demand its follower to do one thing and then it does another, or claim one thing and when it is something else, or that it attempts to force you to suppress/control/coerce you and your family, or (as far as I know) have been used to killed millions (billions?) of people.
As for agnostics, there are plenty of different subdivisions, such as
- does not believe in a god, but will consider evidence
- does believe in god, but will consider evidence
- does not care if god exists or not
- actively search for proof of the existence of god, or the lack of
And when "you" die, your existence doesn't end (otherwise quantum physics is fail). You body will be recycled, no? If you are referring to the "consciousness", then I do believe that's just the end of it. As for the purpose of life, I would stick with the age old chinese proverb, "continuation".