Friend, this is just my own take of what is in the scriptures.
"Now Peter sat without in the palace: and a damsel came unto him, saying, Thou also wast with Jesus of Galilee. But he denied before them all, saying, I know not what thou sayest. And when he was gone out into the porch, another maid saw him, and said unto them that were there, This fellow was also with Jesus of Nazareth. And again he denied with an oath, I do not know the man. And after a while came unto him they that stood by, and said to Peter, Surely thou also art one of them; for thy speech bewrayeth thee. Then began he to curse and to swear, saying, I know not the man. And immediately the [bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse] crew. And Peter remembered the word of Jesus, which said unto him, Before the [bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse] crow, thou shalt deny me thrice. And he went out, and wept bitterly."-Matt. 26:69-75
Look at that passage closely. Peter not only denied knowing Jesus but went as far as to even revert to his former life. He began to curse. As I look at these scriptures, I would suggest that Peter "backslid." But afterward, he went out and cried bitterly. As I look at that, to me that suggests that Peter repented of his sin.
Anybody can backslide. I was a Christian until I was 14 y/o, then I walked away. I stayed out in the world until I was 37. Now, I could not see any way I could do that now. I had backslid. But the difference is that I came back. Just like the prodigal son, I was lost, but now I'm found. I was dead, but now I'm alive.
To me, the only 12 step program you have to take are those steps which keep you separate from God.
Let me put it like this, as long as there is a breath of life left in you, there is hope. Only after you die is there no hope if you don't know Jesus.
The writer of Hebrews knew we couldn't walk without sinning:
"Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us," -Heb. 12:1
Thank God that He made provision for us when this happens:
"If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness." -1 John 1:9
Yes friend, as long as there is a breath of life in us, there is hope. The "backslidden" can be forgiven.