Does the NTSB ever not follow up a preliminary report? Two years ago, there was a fatal crash in Fredericksburg, VA in which 6 people died in a Beech 95-B55. For some reason, the story struck me, and I wrote a note to myself to follow up on it.

The NTSB published a preliminary report 12 days after the crash (on 8/24/2016) but has not published any report since then. Do investigations sometimes end at preliminary reports, or will they someday follow up with a final report?

The NTSB case is ERA16FA288. I searched the NTSB's "Aviation Accident Database &amp; Synopses" page for all events in Virginia on 8/12/2016 (as well as googling the airplane's tail number), and couldn't find anything after that preliminary report.
As a retired NTSB employee, I can say that reports with an FA number like that one should definitely close out with a probable cause determination, typically within a year.  Two years is an outlier, and the delay is likely attracting some internal attention.  If you really want to find out about the status, you can call 202-314-6290 and ask for the Ashburn field office.  It's probably their case, and the manager should be able to figure out what's holding it up.