He has to live on, even after the end. He has to keep the memories of his family in his mind for as long as he could, because in a way he could make up to them for his lateness by giving them the only life he can possibly give.
His predicament reminds me of Randall Clark from Fallout New Vegas, the survivalist who holed up in Zion National Park when his world came to an end in a nuclear holocaust.
He tried suicide for years but didn't do it, despite having lost his family and everything else, believing that living as long as he could and keeping his memories of them is the only way he could atone for not being there for them when they died in atomic fire.
He did however leave behind a meaningful legacy in the form of the Sorrows tribe, whom he protected and looked after, from a distance, when their ancestors (a band of children) arrived at Zion valley in the last years of his life. He died considering them a gift to him after years of loneliness and failure, being able to behold innocence, and he is remembered by them as the Father of the Cave, figure of their mysticism and worship. His story in the game is one of the best tales I have ever read.
Yeah, only knew it myself when I caught it on Tvtropes page and then the Fallout wikia before I actually played the add-on. Made an effort to find all his entries and all his gears.
His terminal entries was what made me decide to side with Joshua Graham and wipe out the White Legs. I couldn't let his efforts go in vain; Zion belongs to the Sorrows and the Dead Horses. Though I did make an effort to convince Joshua not to kill Salt-Upon-Wounds.