Wow that short piece blew me away. One can feel the pain between the lines until it boils over in:

He can’t remember the last time he felt like this, or felt anything at all.

Picturing Clark outliving his family, his descendants and the entire population of earth - if the former weren't already enough - has to be a very sad thing. There are stories which cover parts of that thought but never have I read anything to that extent. This almost eternal life might just be the biggest punishment to be burdened on him.

Also, I can't help but be reminded of a poem I've heard and read years ago from some TV show. There's probably no exact title but it's the first entry on The Poetry of "Space" , a website dedicated to the show Space Above and Beyond.