Are there any sins for which one can never achieve forgiveness, no matter how sorry they feel after the fact? Are there any sins that if one commits, one cannot earn a share in Olam Haba, no matter how much they atone and no matter how many other good deeds they have?

What is the view in the eyes of Hashem of Jews who are raised orthodox and then go off the derech? How does Hashem typically punish those who do? Is the punishment severe? Are they denied a portion in Olam Haba for doing so? Is one who goes off the derech and later returns, either fully or partially, still punished severely for the time they spent off the derech? About half of diaspora Jews who are raised orthodox eventually do go off the derech. So does The All Merciful G-d really bring suffering upon 50% of those raised as Orthodox Jews just because they go off the derech?