I'm going out a limb a little bit on answering this, because (a) my experience in criminal law is largely limited to misdemeanors and non-violent felonies; and (b) I'm not familiar with NC law, at all. Please take my answer with the grain(s) of salt it deserves.
1. I don't think that the lack of ability to determine cause of death precludes homicide charges. I can think of a handful of cases I'm familiar with where homicide charges were prosecuted (some successfully, some not) without a body even being found. A quick google search found me an article discussing 'no-body' homicide prosecutions in NC, specifically in discussion of this case,
here. If you can prosecute a homicide case without a body, you can prosecute a homicide case without a conclusive cause-of-death (particularly when you can't conclude cause-of-death for the reasons in this case, as opposed to other scenarios I could think of).
2. I went to the NC Criminal Statutes (
here) and, even being unfamiliar with NC statutes, found a number of things that might 'fit' (
False reports to law enforcement agencies or officer , a misdemeanor; § 14‑221.1.
Altering, destroying, or stealing evidence of criminal conduct., a Class I felony, are a few that popped out at me). In my experience, prosecutors can get *real* creative in coming up with charges for people. I'm sure someone with more experience in NC law could come up with a lot more.