For all of you still stuck with Lathor to this day, I bring good news: Flix just helped me remove this NPC!
Basically, you have to edit the creatures.txt file in the scripts/server/ folder in order to remove the LUA code that defines him. Search for and then remove this text from the file:
mgr.createCreature {
id = 1687,
itemtype_id = 11067,
name = "Human_Story_Lathor",
behaviour = "questCreatures",
dangerclass = 5,
groupmaxcount = 1,
elite_creature_id = 1687,
probabilityforelite = 0.000000,
rank = 50,
tenergy_creature_id = 1687,
template_creature_id = 1374,
livesremaining = 0,
unconscioustime = 20,
palettebits = "1111111111111111",
monstertype = 0,
faction_id = 12,
equipset_id = 349,
modelscale = 1.150000,
rise_from_ground = 0,
has_corpse = 1,
has_soul = 1,
can_strafe = 0,
}
Do this while the game is closed! Then save the file and open the game again. The game won't be able to find this NPC definition and therefore won't load it. Tadaaa! Lathor is finally gone.
Note however that its quest, "Salesman of Death", will still appear on the map as a souvenir at its starting position, in front of Lothar's house in Badawi. I guess it's a minor inconvenience.
Also, Flix pointed out that if you have not started this quest yet, you should install the Community Patch first. Then, the quest won't be buggy.
Enjoy!