Interestingly, belief in Hashem is not one of the Zayin MItzvos, I think. Not believing in Avoda Zara is, however. (Correct me if I am wrong).
If one does not believe in God, they have no chelek in Olam Habba. Nadda, nothing, zilch.
Source? And don’t bring “Apikores”.
Any “good” that they do in their lives is worthless.
Patently false. Even Rashaim get Schar in this world, so that they need not be rewarded in the next.