We can no more get unborn again than we can get unborn. We can no more undo our spiritual rebirth than crawl back into our mother's womb. What's done is done.
We can abuse it, take it for granted, or try to run away. The flame may flicker, or even "appear" to have been completely doused through rebellion. And in some cases, like the prodigal son, severely and for a very long while.
Better of course if we never doubted or abused the grace of Jesus. But when we do, and who doesn't, our Father will no more cut us off than we would disown our own children.
The Scriptures are replete with this promise. Paul wrote, "For I am convinced that neither death nor life, neither angels nor demons, neither the present nor the future, nor any powers, neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord" (Romans 8:38-39).
And Christ himself put it like this: "I give them eternal life, and they shall never perish; no one can snatch them out of my hand. My Father, who has given them to me, is greater than all; no one can snatch them out of my Father’s hand" (John 10:28-29).
We, or our prodigals, may "appear" to have burned ourselves to the ground. We may even be convinced that we have gone too far to ever again be on fire for Christ. Yet once lit, no amount of bad behavior can fully extinguish the flame of God's eternal salvation.
God has His ways. The Holy Spirit always keeps a pilot light on.
Until every church disciples every man…