Yes, those who fall way are deemed "backsliders". If a person dies in this spiritual condition, he/she would go to hell. So, it's dangerous to fall away into sin, as one may never find their way back to God like King David did. We have no record that his son, King Solomon, ever made it back to God. No doubt there are multitudes in hell right now who turned away from Jesus and never made it back, because a man is far worse than he was before he came to Jesus Christ.
2 Peter 2
[19] ... for of whom a man is overcome, of the same is he brought in bondage.
[20] For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
[21] For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
[22] But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.
But, yes, Jesus would graciously forgive anyone who has fallen away if that person has godly sorrow and repentance for their sin(s), just like the prodigal son.