Xzar and Montaron aren't supposed to disappear at all. Are you sure that your game is clean of other mod remnants? Apart from one time where I did things so out of order that when I tried to drop Xzar and Montaron from the party, they just disappeared, doing things in standard game order worked normally.
I'm more than sure that I use the clean install because I have done it so many times. I attached my ar6600.bcs here. The last part of the fila indicates why they disappear in this area. I've installed BG1, Totsc, the newest patch, and BG2 + ToB with the newest patch. Then, BG2 Fixpack and BGT. Also, I look at the Ar6600.bcs file with Near Infinity, and it seems that thie file is in BG1BCS.BIF which makes me think that this file is exported from the original BG1.
IF
Global("BGTNPC6600","GLOBAL",0)
Level(Player1,1)
THEN
RESPONSE #100
SetGlobal("BGTNPC6600","GLOBAL",1)
CreateCreature("BGXZAR",[4581.2694],0) // 짜르
CreateCreature("MONTAR",[4514.2705],0) // 몬타론
CreateCreature("IMOEN1",[3140.3681],12) // 이모엔
END
IF
Global("BGTNPC6600","GLOBAL",0)
OR(2)
Level(Player1,2)
Level(Player1,3)
THEN
RESPONSE #100
SetGlobal("BGTNPC6600","GLOBAL",1)
CreateCreature("XZAR2",[4581.2694],0) // 짜르
CreateCreature("MONTAR2",[4514.2705],0) // 몬타론
CreateCreature("IMOEN2",[3140.3681],12) // 이모엔
END
IF
Global("BGTNPC6600","GLOBAL",0)
OR(2)
Level(Player1,4)
Level(Player1,5)
THEN
RESPONSE #100
SetGlobal("BGTNPC6600","GLOBAL",1)
CreateCreature("XZAR4",[4581.2694],0) // 짜르
CreateCreature("MONTAR4",[4514.2705],0) // 몬타론
CreateCreature("IMOEN4",[3140.3681],12) // 이모엔
END
IF
Global("BGTNPC6600","GLOBAL",0)
LevelGT(Player1,5)
THEN
RESPONSE #100
SetGlobal("BGTNPC6600","GLOBAL",1)
CreateCreature("XZAR6",[4581.2694],0) // 짜르
CreateCreature("MONTAR6",[4514.2705],0) // 몬타론
CreateCreature("IMOEN61",[3140.3681],12) // 이모엔
END
IF
GlobalGT("Chapter","GLOBAL",3)
Exists("Montaron")
!InParty("Montaron")
THEN
RESPONSE #100
ActionOverride("Montaron",DestroySelf())
END
IF
GlobalGT("Chapter","GLOBAL",3)
Exists("Xzar")
!InParty("Xzar")
THEN
RESPONSE #100
ActionOverride("Xzar",DestroySelf())
END