Um ... I'm pretty sure Sagan was an atheist. It's also not clear to me that Einstein believed in any sort of God that you are advocating.
An eternal Cosmos makes a lot of sense to a lot of people - that's not what you're talking about. You're taking cosmos and imputing properties to it that there is no reason to believe it has. Moreover, btw, it's important to distinguish the idea of something being 'possible' from it being 'likely.'
Everyone, including me, has whatever purpose to their life that they ascribe to it. In short, I agree with Spinoza (a theist with whom Einstein agreed) who said, 'to be what we are and to become what we are capable of becoming is the only end of life.' It's a non sequitur to insinuate that I think the world ends with my existence. No idea how that popped into the discussion.
We're not talking about what rights people have. People have no control over what they believe. Only what they assert. The only question is whether a person professes those beliefs which he actually holds. So I'm not saying you don't have the right to believe that martian mole-men will revive me after I am dead and take me to Nirvana.
I'm answering a question that you asked, namely how can you convince atheists? The answer is - think clearly, write clearly and cogently, and make sense. "Well isn't that nice!" and "Love is wonderful!" aren't arguments.
