It would be very stupid, not to mention disrespecful on your child's part to expect you to keep your promise when he or she did not live up to their part of the agreement..
Why would we expect our Father to keep His promise if we don't hold up our end of the bargain..?
Here is what He tells us..
Heb:10:38:
Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him.
10:39:
But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul.
That should answer the question Loud And Clear..
But remember.. If you let your soul perish, you have no one to blame but yourself..
God will forgive us of all our sins if we will but just truly repent..
That is the reason Christ allowed himself to be tortured and crucified, so that we would have the chance to have eternal life..
He tells us in no uncertain terms what will happen if we don't repent..!
Lu:13:3:
I tell you, Nay: but, except ye repent, ye shall all likewise perish.
So, the question, Once saved, always saved?
Has been answered..