Well, tried many things, but nothing worked. My best guess is, that Kaldor's script didn't fire, because some of the kills where done by the NPC, who is just an NPC and not even a henchman. But on the other hand, the script checks for deaths, not by whom. In any case, this is one of the cases where one can say, "it took too much of my time". I'm afraid I have to go an alternative.
Let the player talk to the NPC after the battle. If not, I will make it so that he appears at the hangout spot no matter what, and the PC might have a dialogue option "what are you doing here, didn't I leave you where we fought?", if the variable for an after battle convo has not been met.
That, I can do

. When I have time, I will look at the matter one more time. But for now I need to get it out of my head to continue on other areas.