would require the DA to not present the case to the GJ. Technically, that determination can be made, and is made all the time. Here, it was a pretty much forgone conclusion that the case would be presented, probably regardless of the evidence, just because of public sentiment. So, regardless of what DJ's testimony is or was, they GJ still has to vote if the case is presented and no one can predict what the vote will be. There is also the Civil Rights case that is being investigated by the DOJ.
Now, if this story about DJ is true, then, yes, it is highly unlikely that the officer would not be indicted by the GJ if the case is decided. It may also be that the DA would decline to present the case, since the closest witness has changed his story. However, changing your story isn't like a postive thing and usually means oyu have to assess credibility. So I doubt the DA will just take his word and decide not to present.
Honestly, I find it hard to believe. This guy has had an attorney from the beginning. It's not "impossible". Maybe DJ is ticked off for some reason. I don't pretend to understand the dynamics present here. But he wasn't the only witness and this is a pretty high profile case to just not present to the GJ if that deicison to present had been made.
I haven't read any defintive source that the GJ is happening. As I said, it's up to the DA. And they don't announce it so no way to know except through leaking.