Hello, thanks for asking your question.
Yes, USACIL takes six months or more to do forensic examinations of media looking for evidence. Yours was likely put on the back-burner because they have much more serious cases involving child porn and sexual assault that need to be done first.
When you were interviewed it's possible you were "titled" and your name put in the CID/NCIC database. If that has been done, there may be an issue if you need to apply for a security clearance or are due for an update.
They are required to return property once an investigation is closed and the property has no evidentiary value.
Thus, the return of the property and the length of time indicates the likelihood to me that the case is closed. As I said, the only potential issue at this time is the clearance.
There is a two year statute of limitations for imposition of Article 15
punishment and a five year statute of limitations for prosecution at court-martial.
The fact that you PCS'd tells me you weren't flagged. Which is a reason you got to PCS and why no-one is looking or interested in your situation.
Absent someone coming forward with new allegations I think the case is likely closed and over.
Lesson learned - stay away from or report people involved in illegal drug use or possession.