If the case can be proved on the basis of other admissible evidence, no, dismissal is not the only outcome. The government has the burden of proof (standard is 'beyond a reasonable doubt') and a missing witness can impact the ability to meet that burden.
Lots of added details are missing from your post to fully be able to suggest all options to you.
On preliminary question to be answered is: "What stage are you at in the process?" If you are at the preliminary hearing stage, the prosecution's burden is to establish a prima facie case which does not require the prosecution to prove the case beyond a reasonable doubt. Thus, they may show a prima facie case with other evidence. More importantly, if the case is dismissed at the preliminary hearing stage, the charges can be refiled.
If you are in Lancaster, ARD is available to you for simple assault/ D.V. cases. Contact my office for more information.