Why will The Giver not go with Jonas ?
After the Giver shows Jonas the video footage of his father lethally injecting an infant during a routine release, Jonas is horrified and appalled with his community. Jonas refuses to go home and ends up spending the night in the Annex with the Giver. That night, the Giver and Jonas come up with a plan that will alter the community's future for the better. Their plan requires Jonas to fake his accidental death while he secretly escapes the community and travels to Elsewhere hidden in a transport vehicle. In chapter 20, Jonas begs the Giver to leave the community with him and accompany him to Elsewhere. The Giver responds by reflecting on how the community reacted to the loose memories after Rosemary's death. The Giver tells Jonas that he must stay behind to give the citizens wisdom and help them cope with the difficult memories after Jonas leaves. The Giver fears that if he leaves with Jonas, the citizens will panic and chaos will ensue, which is why he decides to stay back.
When Jonas decides to leave, he pleads for The Giver to come with him. The Giver responds that he is old and not strong enough for the journey. He also says that the community will need him.
After Jonas leaves, they know he will face harsh conditions. Long hours of running, harsh weather and lack of food would be very hard on The Giver. He would likely slow them down. Gabe is enough of a burden, since he too needs to eat and be kept warm and cannot fend for himself. The Giver has also given Jonas many of his memories, possibly leaving him not enough to sustain himself and them.
The main reason The Giver cannot leave is that when Jonas leaves, all of the memories he has will be released back to the community. Chaos will ensue unless someone is there to help them. With both Jonas and The Giver gone, all of the memories of pain and suffering would go back to the people. They would be confused and not know what was happening to them, and without The Giver there would be no one to help them through it.
After Jonas leaves, all of his memories will be released to the community. The Giver wants to stay and help the community face these memories after Jonas leaves.