I'm putting together a Pascal's wager piece of sorts, and wanted to see what modern religions think atheists deserve. So if Judaism pans out to be the one true religion, what'll happen to me (an atheist) after death?
depends whether you truly investigated the truth on this topic or whether you were just interested in writing papers. if the latter, tremendous burning regret. if the former, God will help you find it. And if He doesn't for whatever reason, though this is unlikely, then it's not your fault.
Here are some relevant quotes on this from a major Jewish philosophical work Chovos Halevavos
Gate of Repentance ch.5 (Pascal like consideration)
The conditions for resolving to not repeat what the Creator warned against are also five: (1) To weigh an immediate pleasure which is fleeting and mixed against a future, constant and everlasting pleasure, pure with no darkness and without any mixture of pain. And to weigh an immediate, fleeting pain, which is without permanence, against a future pain, which is everlasting and without interruption.
Regarding the pleasure (in the afterlife), it is written: "And when you see this, your heart shall rejoice" (Isaiah 66:14), and "the sun of mercy shall rise with healing in its wings for you who fear My Name. Then will you go forth and be rich as fatted calves" (Malachi 3:20), while regarding the pain it is written: "And they shall go forth, and look upon the carcasses of the men that have transgressed against Me: for their worm shall not die, neither shall their fire ever be quenched; [and they shall be an eternal abhorrence unto all flesh]" (Isaiah 66:24), and "For lo, the day comes, that shall burn like a furnace, and all the audacious sinners and all the perpetrators of wickedness shall be stubble. And the sun that comes shall burn them up so that it will leave them neither root nor branch, says the L-ord of Hosts" (Malachi 3:19). When the sinner puts this matter to heart, he will deem it proper to take on himself not to repeat his sin.
and another one from Gate 3 ch3 regarding one who neglects to follow the obligations dictated by his understanding such as an atheist who neglects his duty to fully investigate the truth as to whether there is a Creator and if yes, what does He want from me.
And when he does not accept the duties dictated by the understanding with which he is endowed, and its rebuke, he loses the character of a rational creature; and the cattle understand how to improve their condition better than he does, as it is said, "The ox knows his owner, and the donkey his master's trough; but Israel does not know; My people does not consider" (Isaiah 1:3). Such a person's fate will be like that of one, concerning whom it is said, "But the wicked shall perish; and the enemies of the L-ord shall be as the fat of lambs, they shall be consumed; into smoke shall they be utterly consumed" (Psalm 37:20).
But if it is not one's fault for whatever reason, then the torah exempts one for liability of his actions,as the talmud derives in various places such as Nedarim 27a and as the Chovos Halevavos explains in Gate 5 ch.5 regarding not considering yourself better than a seemingly bad person.
And even if his appearance is bad, it is possible that the reason is because he is ignorant of his obligations to the Creator. Therefore he is more pardonable than me, because my knowledge is greater than his. For the Creator claims from a man only according to the extent of his knowledge. Therefore, I am more deserving to be considered reprehensible for my shortcomings in the Creator's service, despite my knowledge compared, to this man whose shortcoming is due to his ignorance. He rebels against G-d due to ignorance and error, while I rebel against Him knowingly and deliberately.
As you can see it is not a single answer for everyone. Every case will be judged independently upstairs.
If someone believes in doing good because it is right and not merely for personal gain, then they do by definition believe in G-d, at least as Judaism defines it. They are simply defining their terms differently. Did you know that when the Romans would sentence a person to death for becoming a Jew, the crime was called, "atheism"? Since the Jewish G‑d cannot be seen or described, they considered this person to be without any god at all. Turns out that Judaism is closer to atheism than most people's theism. As Rabbi Sholom Dovber of Lubavitch once put it, "The G‑d the atheist doesn't believe in, I don't believe in either."