(NOTE: Some spoilers for "Strictly Business" and "Rescue from Paradise")

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..

Missing Scientific Puruits is most likely because you skipped some portion of the main quest.

Some unnamed NPCs will respawn after 73 hours have passed, but once a named NPC is dead they stay that way. If you are on PC then I believe there is a console command you can use to bring them back to life, but if you are on xbox or ps3 then your only options are loading an older save or starting over.