Half the point of GTA V being set in Los Santos was so that we could drive around the opulence of Bel Air and the Hollywood Hills. I don't know if Rockstar ever meant for part of the city to be transformed into a post-apocalyptic scene like something out of The Last Of Us. There are two mods at work in this video. The map is by Rapidiment, and takes a section of the Los Santos city centre (it's a smaller map made for making videos, not the entire game world) and wrecks it all up. The Joel skin was inspired by the map, and is by GTAFREAk67S.
Note this doesn't add burly bearded survivalists and shambling plantmen to the game. If you need something undead to shoot at, you could maybe try this zombie mod. Or just enjoy the peace and quiet and pretend Life After People had a very slick video game tie-in.