Are charges dropped?

The prosecution may drop the charges. The other possibility is that prosecution seeks an adjournment, in the hope of getting their witness to turn up next time. But court will want a very good explanation as to why witness isn't here, and why it would be fair to defendant to grant an adjournment. High chance that outcome is that prosecution can't satisfy court on this point, adjournment is refused, charges are dismissed.

There's a theoretical possibility that the prosecution proceeds without the evidence of the victim, and the evidence of other witnesses is sufficient to secure a conviction. But I don't think that's a very likely outcome in real life.