I'm sure this concept is part of a larger fix or tweak pack, but I can't find it individually quickly with a forum search or a google search, so I'm posting my fix here. I modified the HAPPY.2DA file so that a value that typically lets characters know it's time to leave due to low/high reputation doesn't trigger. It can be installed by dropping in to your override folder in C:\Users\[YourUserNameHere]\Documents\Baldur's Gate - Enhanced Edition\override. If that folder doesn't exist, you can create it and drop the attached HAPPY.2DA file in it. The location of where your override folder should be may be different depending on your operating system. It should stop NPCs from leaving due to reputation being too low or too high.
I know this exists in some other mods, but personally I prefer to install individual fixes myself. This is mostly for people who share that attitude and would rather drop a file in the override folder than let an exe or other mod distribution platform change whatever else it is they are going to change.