In Fallout 3 I met Paladin Hoss and another guy fighting super mutants, and they recruited me to follow them in finding their teammate. But after a minute or so, he got blasted and died by one of the mutants. Is there any way to replay the mission as it seems to be a good opportunity for farming? (good xp, items etc.) I play the ps3 version, so no console commands are available I believe.
There is no in-game way to reset quests in Fallout 3. If a quest specific NPC dies, the only ways to do the quest would be using console commands (which, as you said you don't have) or loading a previous save.