Evil NPCs only dip out at 19+ reputation in either game.
As for Dorn, when I reached 19 rep he actually just acted like I had manually removed him from the party, and I had the "nevermind" dialogue option to keep him around. I assume this was a bug or an oversight, though, and it may be fixed by now.
Dorn will leave when your rep goes too high, I've had a bug after that happens to my group when I load a game upon loading that he'll act as if I'm asking him to leave since I lowered my rep and got him back in my party.
getting caught while stealing..killing some random ppl; the latter penalty depends on your current reputation. edit: http://stane0.tripod.com/BG1Tables.html - lower part of the page..the values should still be the same, as getting the rep higher via donation uses also this tables. (BG2 amount of gold is different)
About the leaving: I think if you can manage to get an evil NPC to join your party, while your rep is already 20 (and that needs a decent CHA score as well) they won't leave. The trigger is only the change to the reputation, that causes them to go bye-bye.
That's from various BG2 discussion, but never bothered to confirm it myself. At least Viconia (BG2) is tricky as you'll get a penalty hit with her joining afair.
Comments
As for Dorn, when I reached 19 rep he actually just acted like I had manually removed him from the party, and I had the "nevermind" dialogue option to keep him around. I assume this was a bug or an oversight, though, and it may be fixed by now.
edit: http://stane0.tripod.com/BG1Tables.html - lower part of the page..the values should still be the same, as getting the rep higher via donation uses also this tables. (BG2 amount of gold is different)
About the leaving: I think if you can manage to get an evil NPC to join your party, while your rep is already 20 (and that needs a decent CHA score as well) they won't leave. The trigger is only the change to the reputation, that causes them to go bye-bye.
That's from various BG2 discussion, but never bothered to confirm it myself. At least Viconia (BG2) is tricky as you'll get a penalty hit with her joining afair.
very helpfull table(s)