I think Jonas safely travels out of the community and finds other societies unlike the one depicted in The Giver. Jonas demonstrates bravery throughout the novel, giving him the courage to escape. He also is intelligent and appalled when he begins to understand what type of place in which he lives. For example, he does not want to return home when he understands "release" means putting someone to death. After watching his father release an infant, Jonas is repulsed.
As for the community, it would have been thrown into disarray. As the Giver noted, there was no one who could take over Jonas' job, and clearly the Giver lacked the heart to transfer painful memories to someone else. His reluctance probably stemmed from training his own daughter, who sought release as an escape from the torture of bearing the community's memories. After the Giver lied and told the community that Jonas had died, "Their attention would turn to the overwhelming task of bearing the memories themselves. The Giver would help them."
This question has been asked and answered quite often here on eNotes. Here is a link for you: http://www.enotes.com/giver/q-and-a/what-happens-end-giver-any-proof-137461