Your nephew does not always have the right to testify at trial. First of all, you need to make sure there is no evidence that can be independently authenticated without victim testimony. If that is the case, then you need to look at whether or not there were other witnesses to the event. If neither of these things are present, the prosecutor has only one option, and that is to subpoena the victim. If the prosecutor is successful at subpoenaing the victim, then they must show up and testify or they could be subject to a material witness warrant. If the victim cannot be subpoenaed, there is a chance they could dismiss at trial.
I have seen so many people screw this up on their own and end up with convictions. Do yourself a huge favor and call private counsel. My office offers free consultations.
Who called the cops? As Tom mentioned, if the victim doesn't show up but an independent witness does respond to the summons... then you can still be convicted.
Also, battery doesn't require any amount of damage - just the unwanted touching is usually enough to convict. NRS 200.481: "Battery" means any willful and unlawful use of force or violence upon the person of another.
Clark County, Nevada practitioner.
You should do exactly as Mr. Boley suggests. The last thing you shlould do is discuss the case with your nephew or any other person who was a witness. This at best only taints their testimony at worst you could get new charges for disuading a witness.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.