Chapters 21-23 are the last three chapters in The Giver where the climax and resolution are found. The Giver and Jonas had come up with a plan for Jonas to escape and the Giver would help the community deal with all of the memories that would consequently overwhelm them. The plan had just been devised before chapter 21, so they were going to think about it more and come up with the details later. Surprisingly, however, Jonas finds out at dinner that Gabe is scheduled to be "released" the next morning; so he takes Gabe that night and forces the plan into action early. The rest of chapter 21 is about Jonas feeding and giving comforting memories to Gabe while avoiding planes that are searching for them overhead.
Chapter 22 shows Jonas and Gabe still on the road but the geography is slowly changing, as shown below:
"All of it was new to him. After a life of Sameness and predictability, he was awed by the surprises that lay beyond each curve of the road. He slowed the bike again and again to look with wonder at wildflowers, to enjoy the throaty warble of a new bird nearby, or merely to watch the way wind shifted the leaves in the trees" (172).
Jonas and Gabe start to experience starvation due to unanticipated length of the journey. Jonas tries to give Gabe memories of eating food to satisfy him, but it doesn't work for long. Both Jonas and Gabe cry because of starvation and exhaustion.
By chapter 23 the boys are cold and freezing. Snow is falling and there seems to be no hope left, even if Jonas feels like the end is near. They are dirty and starving and don't know where to go. Jonas gives Gabe memories of warmth to sustain him as they trudge through the snow, but those don't last long--nor do they help to remedy the reality of the situation.
Jonas's mind goes over his own experiences with Asher and Fiona. He thinks over his life and finds a little bit of renewed hope to keep moving. Eventually Jonas finds a sled and they slide down the hill. He thinks that he hears people singing as he slides down the hill.
The book ends there. There is no textual evidence, explicit or implicit, that shows Jonas and Gabe actually make it to anywhere safe. The text does say that they go in and out of consciousness. Jonas is down to his last memory, which happens to be the first one of the sled. This suggests that after this memory, there's nothing left to help the boys unless they do find someone to help them. But the book ends with this:
"Behind him, across vast distances of space and time, from the place he had left, he thought he heard music too. But perhaps it was only an echo" (180).
The question of whether or not Jonas and Gabe survive is left to the reader to determine.