It's probably been said, but haven't read through the 20+ pages. But YES, you can fall short of the grace of God as said in Hebrews:
"Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled;"
Esau fell from Grace, repentance was not found
Judas fell from Grace, committed suicide.
Saul fell from Grace, committed suicide. **NOTE** God said in Chronicles that he SLAYED him. Even though Saul took his own life, God took the credit for his suicide.
Hymenaeus made his faith shiprwreck
Demas loved this present world and forsook the faith. Maybe was sinning wilfully.
Hebrews 6:4 SCARY
Hebrews 10:26 very SCARY
1 John talks about the "sin unto death" by which prayers are not even suggested to be given for such a person.
Jesus said you can "lose your salt (savor)"
Jesus said, you can be "cut off" the vine (dead branch)
Paul said, KNOW YE NOT that Christ is in you, UNLESS you be a reprobate.
Being given over to your sin....shows you are rejected silver/reprobate. Romans 1.
I could go on and on, but YES you can fall from grace and fall short of God's grace. AT that point, you fall in the hands of God who is a consuming fire.