I agree the case becomes weaker, maybe impossible based on missing evidence. But missing evidence doe not per se mean the fact the evidence is missing can't come in to the trial. The people who saw it (the evidence, before it went missing) can testify they saw it. That is not hearsay.
If the recording is the only evidence (well, recording plus the fact that some sworn officers saw it), and the recording is missing, a prosecutor would not bring a case. Not because there is literally no evidence, but because even though the recording was viewed, there is ample room for reasonable doubt the allegation is true.
What about testimony say from 6-8 NYPD Commissioner etc. personnel that the copies they still retain are authentically and exactly what the original contained?
Actually, it is. I spent a year as the foreman of our county's Criminal Grand Jury and as part of that we were asked to hear a murder case as a mock petit jury to find out if they had enough to arrest the prime suspect under their theory of the case and get a conviction beyond a reasonable doubt (they could not we determined).
I sat as the judge during the whole thing with the assistance of a retired superior court judge. Part of the problem was that ten years had passed since the murder had been discovered and the county sheriff's office had moved from one building to a new headquarters building. Some of the original evidence got lost in the move. The prosecution had photos of that evidence, and officers who SAW the evidence would testify about the evidence, but the judge assisting me said it could only be given the same weight as hearsay evidence without the original evidence. i.e. not much. Because, he said, the defense would not be able to examine it and that can lead to reversible error. Without the original evidence, with an unimpeachable chain of custody, which can be examined by the defense, secondary claims about that evidence even existing may just be thrown out.
We determined that their theory of the murder could not be proved beyond a reasonable doubt but the prime suspect was certainly guilty. However, I wrote an alternative theory which I gave to the primary investigator based on the evidence to pursue. Five years later they arrested the suspect and he pleaded guilty to reduced charges but had to elucidate exactly what he had done as part of the plea.
It turned out the murder occurred exactly the way I had outlined to the detective. It was the only way it COULD have been done to account for the evidence.
Someday I am going to turn the story into a Movie script.