What is the plan Jonas and The Giver come up with in The Giver? And how does it change?

In their original plan, The Giver and Jonas planned for Jonas to escape from the Community in two weeks, on the night before the December Ceremony.  During those weeks, The Giver would transfer his memories of courage and strength to Jonas, so he could use them to find Elsewhere.  Jonas would sneak out of the house at midnight, when no one would be out on the streets.  He would take his bike to the riverbank and leave it there with some folded clothes, to make it look like he had gone for a swim in the river and drowned.

Jonas would then go to the Annex, where he would hide in a vehicle The Giver would have ordered to transport himself to one of the outlying communities he frequently visited.  Jonas would ride the vehicle until he was well away from his Community, and then make his way on his own (Chapter 20).

The plans change when, that night, Jonas' Dad announces that Gabe is scheduled to be Released the next morning.  In a desperate attempt to save the child, Jonas steals away that night, taking his father's bike and Gabe along with him.  There is no time to say good-bye to The Giver, but Jonas feels he will understand.  Peddling frantically by night and hiding by day, Jonas eludes the seach planes which have been sent to find him.  He and the baby approach what Jonas believes is their destination with the last remaining strength remaining within them.  The book ends ambiguously; finally, it is not clear whether Jonas and Gabe make it to Elsewhere or not (Chapter 21).