It's possible, in general I wouldn't expect it. But certainly cases of that occur. There are some very moral atheists. I knew two wonderful people, nice as can be, who didn't believe.
But the thing is, just being relatively moral is not going to help them. They'll be judged by a perfect Holy God/Creator who knows no sin. And He is going to judge us by His own perfect standard. Not by some Bell curve of human goodness, where if you're closer to Mother Theresa than to Adolf Hitler, you're ok.
Scripture calls us to "Be Holy for I am Holy.", "Be perfect for I am perfect". There are only two ways to stand before such an awesome Holy God and live. Never sin, or be forgiven. Atheists will be judged by their works. And their evil deeds, even if they are few in number will condemn them.
God who knows the future, has already declared, "None are righteous, no not one.". But He also holds out the promise, "Come let us reason together, though your sins are like crimson, they shall be whiter than snow."
Those two people, were extended family members, in their 70's. Not the kind of people you expect to change. But we began praying for them regularly. Four years later they accepted Jesus as their Savior. Awesome!
Which is the more moral person.
The atheist that lives a moral life because he is considerate of his fellow humans or the non-atheist that leads a moral life so he will go to heaven?