I have not read the books and only watched the movie, so I might be missing some crucial explanation, but why would memories be released if the the Receiver leaves the community? Is it a safeguard of some kind? If so, shouldn't it be the same in case Jonas or the Giver simply die, without any need to go far away?
Having both seen the movie and read the book, I think I can satisfactorily answer your question:
The return of the memories in the film, and the entire "boundary of memory" concept is a massive plothole due to inexplicably changing several concepts from the novel.
- The memories return if the Receiver dies:
In both the book and the movie, there are references to the prior receiver-in-training applying for retirement, and causing a minor calamity upon her death. In both stories, it's explicitly stated that her death caused the memories she'd acquired to be returned to the community. This is why receivers-in-training are forbidden from applying for retirement.
- Leaving the Community also causes the memories to return:
In the book, it's explained that the further Jonas gets from the Community, the more the memories/emotions will return to the people. In the book, he regularly has to hide with Gabriel and pass along memories of snow, which lowers their body temperature enough to hide from thermal-imaging planes that are seeking him out. As he progresses, he has fewer and fewer memories to impart-- but we never learn for certain whether or not the memories have returned to the Community as planned, or if he's just losing them because he's transferred so many to Gabriel.
- The Chief Elder's plan is utter nonsense:
After it has already been established that the receiver either leaving or dying will cause the memories to return, the Chief Elder orders Asher to kill Jonas. This would immediately cause the memories to return to the Community, and makes no sense either by the novel's logic, or the film's.
I don't know about the movie, but in the book, the memories are released if the Receiver dies. This is the former Receiver becomes the Giver when Jonas is assigned to the role. He gives his memories to Jonas, and loses them in the process, so that when he eventually dies, those memories are not released.
The exact mechanism by which memories are stored and transferred is not specified in the book, nor is the method for suppressing feelings. It is implied to be connected to the community's location, but only by the fact that leaving would release the memories. So I can't really help with why leaving releases the memories.
Also, the ending of the book is ambiguous, implying that
Jonas may have frozen to death some time into his escape.
The sequels answer that definitively, though.