The case may also have to be dismissed because of some technical failure of the evidence, or because the defendant cannot be found or is considered incompetent to stand trial. None of the reasons means that the witness are unimportant or unnecessary, or that their willingness to testify is not appreciated. The presence and willingness of witnesses to testify may be the deciding factor in determining what will be done in the case, particularly in getting the accused to plead guilty. Such a person is obstructing justice and may be committing a crime. Call the law enforcement officer in charge of the case.
Police can ask the judge to issue a new warrant, or to revoke the defendant's bail.
The witness may refuse or can talk. It is the decision of a witness. The defendant in the case may decide to plead guilty. The plea may only come at the last moment before trial, often because the defendant's attorney is hoping that a witness will not show up, or that the case will be dropped for other reasons. In a trial, the prosecutor presents the case for the State, attempting to prove beyond a reasonable doubt that the defendant did commit the crime as charged.