If the victim doesn't show up to testify at trial what will happen to the case?

It could be dismissed. Remember murder cases never have victims and the case goes on. In the normal robbery if the victim does not appear there is little evidence. The State could move under new rules of evidence for a intimidation exception. That exception is new and tough to get. If successful the State could submit her statements to police. But normally Crawford v, Washington will apply and you have to be confronted by your accuser. If you confessed there would be some interesting issues to debate. I believe you have an attorney, ask your attorney.

As usual, my colleagues are correct. You need to discuss the matter with your lawyer and if you do not yet have one you need to get one ASAP.

I agree with my colleagues, the state can proceed with charges, but would have a better case with the witness available. You should have no contact whatsoever with the victim. Like the others, I highly recommend you have counsel handle this.

If the matter is post Grand Jury and Trial ready, the State will likely seek an adjournment or adjournments in order to obtain the cooperation of the alleged victim. Clearly I would expect you should have an attorney at this point. If not, you must apply for a public defender or obtain private counsel immediately. If the matter is trial ready, the State may subpoena the alleged victim and compel his/her appearance especially for an alleged crime in the 2nd degree. Regardless, you need to consult with counsel immediately as it would seem you may be confused by the pace and/or status of the case. Next, be careful what you divulge in writing as any statements made by you orally or in writing may be used against you.