The creature carrying Foebane is GORSTA01, and the area script controlling the encounter toughness contains the following snippet :
IF
Global("SetDifficulty","AR3001",0)
Global("StartMP","GLOBAL",0)
OR(3)
NumInPartyLT(5)
GlobalGT("XPGiven","GLOBAL",500000)
LevelPartyLT(14)
THEN
RESPONSE #100
SetGlobal("SetDifficulty","AR3001",1)
ActionOverride("gorsta03",DestroySelf())
ActionOverride("gorsta04",DestroySelf())
ActionOverride("gorsta05",DestroySelf())
ActionOverride("gorsta06",DestroySelf())
ActionOverride("gorsta11",DestroySelf())
ActionOverride("gorsta12",DestroySelf())
SetGlobal("SPRITE_IS_DEADgorsta03","GLOBAL",1)
SetGlobal("SPRITE_IS_DEADgorsta04","GLOBAL",1)
SetGlobal("SPRITE_IS_DEADgorsta05","GLOBAL",1)
SetGlobal("SPRITE_IS_DEADgorsta06","GLOBAL",1)
SetGlobal("SPRITE_IS_DEADgorsta11","GLOBAL",1)
SetGlobal("SPRITE_IS_DEADgorsta12","GLOBAL",1)
SpawnPtActivate("SpawnPoint5")
In conclusion, even if you took a level 1 druid in there (you suicidal fool
), Foebane would still be obtainable, as GORSTA01 is unaffected by the difficulty script.