I liked how he concluded in his "last entry". Hopefully, he found some peace at the time he wrote it. Very nice for immersion.
The Survivalist is clearly the Sorrows "God" and I think you are supposed to take the whole thing to mean he lived out the last part of his life helping and protecting them. A lot of speculation is that the kids he mentions are the ancestors of the Sorrows tribe. So a nice turn of events for him at the end of his life.
Some others have suggested a link between the plane and the children, i.e. a Lord of the Flies scenario. In the Lord of the Flies a group of children are stranded on an island after a plane crash. The backstory is that they were being ferried away from a war.