The NFLPA will have a field day getting revenge on Goodell if he oversteps on this investigation. If he hands down discipline when the police aren't pursuing charges, Zeke will file an appeal and this thing turns into an even bigger clustercuss than deflate gate.
Charges aren't necessary for Goodell to hand out punishment.
The policy states: If you are convicted of a crime or subject to a disposition of a criminal proceeding, you are subject to discipline.
But even if your conduct does not result in a criminal conviction, if the league finds that you have engaged in conduct [prohibited by the policy], you will be subject to discipline."
With domestic violence being an area of emphasis for the league right now, there was no doubt that this would be investigated and Elliott better be squeaky clean or the league can punish him. The league knows that it handled the Ray Rice incident poorly and has been trying to go out of its way not to do that again. (Its attempt to suspend Hardy for more games than allowed is an example of that.)
In a way, domestic violence is the worst thing that Elliott could be accused of right now, so he better be squeaky clean.