Now and then, the K'hara does discuss as you said above. Again there have been times where they only one line kill, but if they tend not to kill you within the first three seconds that you see them, then they probably will be willing to make you extremely scared with visions (thats what usually happens) or something along those lines.
to sum it up, the K'hara CAN roleplay, its not like its impossible for them to do so, and they CAN let you go if you give them a reason to let you live. This may be a little difficult, but its not unheard of. Its not like there's any obligations that they have to kill you.
