The victim can not withdraw the charges, they are not technically parties to a case, they are witnesses. The case is typically the state vs. the individual. They can ask that prosecution be dropped or recant their allegations, but prosecutors get the final call, they have to decide if they feel they can prove the case.
They can not.
This is true.
If the eyewitness was served with a subpoena for trial and then doesn't show up, thus violating the subpoena, you would ask the judge for a mistrial on that basis; you have to have served them, though.
Unfortunately it happens a lot.
Not really directed at you, but since you used the "innocent until proven guilty" line, I wanted to address that quickly. Innocent until proven guilty only applies to taking somebody's freedom away. People are not "innocent until proven guilty" in any other context, and you see us, in society, not hold to that standard all the time. OJ Simpson. Casey Anthony. Trump and/or Biden right now. You even see it in lesser circumstances like people making judgments on the athletes competing based on our very limited information. People getting fired based off accusations. It's fine. The court of public opinion does not have that standard, nor is it required to. Part of being human is we form opinions.
Both statements are incredibly, incredibly false. Ann Coulter's reasoning is terrible and biased, and her research skills are not provable based on what you've offered here. There are many, many twit attorneys.