[SixOfSpades]

In your first post, you said "we" killed the slave guy in the Copper Coronet. If Hendak doesn't get the killing blow on Lehtinan, he might turn Hostile to you, and sometimes bystanders will turn Hostile if you hit Lehtinan at all.

Once Hendak kills Lehtinan, he remains glued to that spot for the rest of the game, unless of course something attacks him. (He might come to your aid if hostile creatures, such as Bandits, follow you inside the building.) So if he's not by the bar, then that probably means that you killed Lehtinan while Hendak was still wandering the hallways in the Coronet--which means that congratulations, you've buggered the quest, and it's way too late to do anything about it now.