Jacob accompanies you during the Plik's Safari quest, and helps you fight off feral ghouls. He will most likely die during the course of the Safari, unless he is reverse-pickpocketed higher level weapons and armor. If he survives the initial Safari, he simply disappears from the game.
If he survives, he will say "Mr. Plik has done it again" (although he also says this before starting) hinting that he may have managed to survive a safari before. However, most would assume that is not possible because of his poor stats.
He actually has great Small Guns skill, but his health is only marginally higher than average, making him unsuited for surviving prolonged combat.