If the witness is under subpoena, s/he is required to go to court. A subpoena is a court order. If disobeying a court order, you can result in the witness being arrested, pulled into court against his/her will, made to testify, and potentially jailed for contempt of court. On the other hand, if the witness has not been subpoenaed, then the witness may do whether s/he likes.
Whether the State can prosecute you without the witness' cooperation depends on whether there is other evidence proving the battery charge. If someone else saw the incident, if there is video of the incident, or if you confessed to the charge for some starting examples, the prosecution may not need the witness. There is simply not enough information here to answer this part of your question.
You need a lawyer. Do not rely on the witness' not showing up as your sole defense. S/he may have a change of heart or there may be other evidence to prove the case against you. A knowledgeable, experience, caring lawyer will be able to help guide you through this morass.
Having practiced criminal law in and around Gainesville for many years I can say the prosecutors will make every effort to ensure people who live out of state show up. They will pay for airfare and take other steps to get witnesses to court. The witness could get in trouble if they were subpoenaed and don't show, but there are very specific procedures that have to be followed to subpoena an out of state witness and the prosecutors in Gainesville don't always follow them. Bottom line, talk to a lawyer about all the facts of the case so that they can give you specific advice about how to obtain the best possible result.
This answer is provided for informational purposes only. The response given is not intended to create, nor does it create, an attorney-client relationship. Each case is fact specific, and it is impossible to evaluate a legal question without a review of all the facts at issue. If you are looking for legal advice regarding a problem in the State of Georgia you may contact my office so that we can set up an office or phone consultation to fully address your question. http://www.kimmeylaw.com
First of all, if you are in contact with the victim do NOT be encouraging that person to not show up. That could bring charges much more serious than the ones you're facing. Often times in that situation I will take a case to trial to see if the victim does, in fact, show up. If they do not, it will most likely be dismissed for want of prosecution (lack of prosecution).