The Jaheira/Harper/Terminsel quest is very buggy. So if you KNOW you've done everything right and KNOW that you are waiting too long for his appearance already you might as well spawn him yourself. There were several threads about that issue here IIRC and you could take a look at Manveru's Jaheira page or the RomancingGuide at sorcerers.net to get a hold of the important variables.
So if you are impatient just clua the old fella in
