The charges will be interesting.
There is no law in N.C. that says you have to be a "good samaritan" - i.e. help someone who needs medical attention.
Unless they can prove that he drugged her without her consent, I can't see any charges being brought against him related to her death. But, if the drug use was consensual and she died from a drug overdose or a combination of drug/alcohol overdose, I don't think there are any charges they can bring against him related to her death.
Plus, let's say the rape kit comes back with his DNA found on her. It would be hard for him to be charged with raping her because she left with him willingly, went to his house with him, went to her apt. with him, apparently drank and did drugs with him - all voluntarily.
Now, I can see charges for improper disposal of a body (or whatever the term may be), concealing a death, hindering an investigation, using a controlled substance, unlawful flight to avoid prosecution, and auto theft (since his car was stolen). So, he'll be going to jail, but I don't think it will be for kidnapping, rape, murder, manslaughter or negligent homicide.