I finished the "main story" about 2 years ago and didn't read any trophy guides etc back then. Well, during "Rescue from Paradise" I probably also received "Strictly Business" -quest, since I have the slave collar and some notes with me (and Strictly Business -mission is listed "grey" (inactive/done) in the list). Back then I basically killed every single slaver in Paradise Falls - probably including Grouse (important when it comes to "Strictly Business").
Well, I'm back into the game now - gathering trophies and doing side quests/DLC. With "Strictly Business", I went back to Paradise Falls. Everything is still quiet and people are dead. No Grouse when you arrive at Paradise Falls.. I have some older saves (probably around lv. 7-8), but not before "Rescue from Paradise" (AKA slaver killing spree for me).
So this probably means, that if I want "Strictly Business" -trophy/quest, I need to start a new game? I guess those dead slavers (Paradise Falls) won't come back to life, like some other enemies in the game (after some in-game time, that's)?
Ps. I also missed the trophy for "Scientific Pursuits". Can't recall what I did wrong..