Because it is common for victims to recant their allegations of abuse out of fear for their safety, pressure from family or friends, or out of mistrust of the criminal justice system, an alleged victim's statement that nothing actually happened alone will not be sufficient to convince a prosecutor drop charges. A victim does not file charges against the defendant, the State does. Similarly, a victim has no control over "dropping charges" if the prosecution saw enough evidence in the case to proceed in the first place. The alleged victim's statement is only a portion of that evidence. Since an alleged victim is not a party to the case, but is only a witness, not showing up in court will have little affect on the case unless he or she is the sole witness and the prosecution cannot proceed without his or her cooperation. In lieu of physical presence, the alleged victim's written statement may be admissible depending on the reason for his or her absence from trial. If there is a history of abuse, the prosecution will likely try to do everything possible to proceed in the absence of the alleged victim's presence if at all possible.
Charges are not automatically dismissed if an alleged victim fails to show up at trial. Assuming the alleged victim/witness was properly subpoenaed and this was her first non appearance, it is likely that the court would grant a continuance if requested. The witness could also be charged with contempt of court for failing to appear.
Assuming the witness appears, It is probable that the prosecution will have some idea about whether she will be cooperative at trial. If the witness testifies that nothing happened, the prosecution will likely be prepared to attempt to impeach her credibility.
The facts you describe are not uncommon in domestic violence cases. Your friend should discuss the specifics with his attorney.
More than impeach credibility, the prosecution will use the alleged victim's prior statements as evidence against the defendant, your friend.
If the alleged victim testifies in court that she lied initially to the police to get your friend in trouble, then the prosecutor will call the officer (or officers) who interviewed the alleged victim initially to testify about her prior statements. Those prior inconsistent statements are evidence against the defendant, not just credibility attacks.
The prosecution does, generally, need the live testimony of the alleged victim to get a conviction. They cannot use police reports or police testimony about what the alleged victim said (unless the alleged victim has already testified inconsistently).
So the prosecution needs her there. But the prosecution will likely get more than one chance to get the alleged victim to come to court.
It is a crime to prevent or dissuade someone from appearing in court.
My answer to your question is based on the facts that you provide in your question. Additional factual details about your situation could change my answer completely. The law in inherently uncertain and always subject to change.