Will simple assault charges be dropped if the victim does not testify?

Possibly. The DA will probably continue the case and tell the cop to get the victim. It may even be continued a second time if the victim shows up. If it is a serious case, the DA will pressure the cop to get the victim into court. If not, the case will eventually be withdrawn or dismissed if you have an attorney. If you don't have an attorney you may get pressured into pleading to a summary. All sorts of things can happen to you. It will go better if you have an attorney.