Marburg: Or people you care about will start to die.
Madison: Mike! Mike!
If Madison is killed and Mike knows that she's Alan Parker's daughter, then Mike can tell Parker that Marburg killed his only daughter. It's the only time Parker doesn't show an emotion that's either a smirk or unemotional crotchetiness - instead, his face collapses in genuine grief, before he tells Mike to go away.
Killing Sis aboard the yacht, because on the news after her death, she gets mistaken for a prostitute and the newscasters speculate that she might have been lured aboard the yacht by a wealthy owner for the purposes of making a "snuff film".
Mina's death, whether you don't rescue her or kill her yourself (You Bastard).