I wouldn't say RC's expression was "stone cold." He's a man in handcuffs, shackles and a prison uniform being transported in public in front of cameras to hear that his daughter is almost certainly dead. On camera, we get a 5-10 second glimpse. I don't believe it is possible to determine what people are thinking and feeling based on that brief observation in that circumstance. Many people, especially males, do not care for messy public emotional displays.
If Haleigh overdosed, the question would be whether it was accidental (she opened a drawer and found pills and took them), negligence (Misty and the boys were doing drugs that they left in reach of Haleigh and she took them while unsupervised), or deliberate (Misty wanted Haleigh to go to sleep for a while or Misty wanted to hurt Haleigh, for example). Ron would certainly have moral culpability just for having drugs on site with small children, but he is already morally culpable for the decision to leave the kids with Misty (as Flora Hollars pointed out very cogently last night). RC would not be legally responsible for Haleigh's death in my view, since he did leave Haleigh with a person over 18. The parents of children who were killed by babysitters, negligently or deliberately, are not prosecuted for choosing a bad sitter. Ron is already under arrest for the drug charges; I suppose it is possible for him to be charged with "endangerment," but I don't see that happening. All this, of course, follows "if Haleigh overdose."