The last couple of times I've gone through Hickory Branch theres's been no Boonthag - is there something that tiggers her (and her gnoll pal) to appear/not appear ?
Can you post savegames to demonstrate this? One from before going to HB, and one after (in which Boonthag isn't there). Each save is comprised of 4 files - *.gsi, *.co8, *.tfaf, *.tfai Pack them into a zip file and upload either here (if smaller than 400kB) or mediafire / rapidshare.
One thing I have encountered in previous plays if if you did not talk to each of the minions and wait for the seal on the cave, they minions will not be in the final battle. They will usually show up as you EXIT the cave and make for a quick slice and dice. Not sure if this is what happened to you moav.
I wondered if that might be the case , I've been attacking them before they can begin their speeches lately - when I leave the cave I do get jumped by the kobold chief and an orc (who runs away instead of attacking for some reason) but no Boonthag